diff --git a/web/src/main/kotlin/world/phantasmal/web/Main.kt b/web/src/main/kotlin/world/phantasmal/web/Main.kt
index 0f23fc22..75f86556 100644
--- a/web/src/main/kotlin/world/phantasmal/web/Main.kt
+++ b/web/src/main/kotlin/world/phantasmal/web/Main.kt
@@ -18,6 +18,7 @@ import world.phantasmal.core.disposable.disposable
 import world.phantasmal.observable.cell.mutableCell
 import world.phantasmal.web.application.Application
 import world.phantasmal.web.core.loading.AssetLoader
+import world.phantasmal.web.core.persistence.LocalStorageKeyValueStore
 import world.phantasmal.web.core.rendering.DisposableThreeRenderer
 import world.phantasmal.web.core.stores.ApplicationUrl
 import world.phantasmal.web.externals.three.WebGLRenderer
@@ -58,6 +59,7 @@ private fun init(): Disposable {
     disposer.add(
         Application(
             rootElement,
+            LocalStorageKeyValueStore(),
             AssetLoader(httpClient),
             disposer.add(HistoryApplicationUrl()),
             ::createThreeRenderer,
diff --git a/web/src/main/kotlin/world/phantasmal/web/application/Application.kt b/web/src/main/kotlin/world/phantasmal/web/application/Application.kt
index 7213b55f..5d0cda69 100644
--- a/web/src/main/kotlin/world/phantasmal/web/application/Application.kt
+++ b/web/src/main/kotlin/world/phantasmal/web/application/Application.kt
@@ -14,6 +14,7 @@ import world.phantasmal.web.application.widgets.MainContentWidget
 import world.phantasmal.web.application.widgets.NavigationWidget
 import world.phantasmal.web.core.PwTool
 import world.phantasmal.web.core.loading.AssetLoader
+import world.phantasmal.web.core.persistence.KeyValueStore
 import world.phantasmal.web.core.rendering.DisposableThreeRenderer
 import world.phantasmal.web.core.stores.ApplicationUrl
 import world.phantasmal.web.core.stores.UiStore
@@ -25,6 +26,7 @@ import world.phantasmal.webui.dom.disposableListener
 
 class Application(
     rootElement: HTMLElement,
+    keyValueStore: KeyValueStore,
     assetLoader: AssetLoader,
     applicationUrl: ApplicationUrl,
     createThreeRenderer: (HTMLCanvasElement) -> DisposableThreeRenderer,
@@ -34,7 +36,7 @@ class Application(
         addDisposables(
             // Disable native undo/redo.
             document.disposableListener("beforeinput", ::beforeInput),
-            // Work-around for FireFox:
+            // Disable native undo/redo in FireFox.
             document.disposableListener("keydown", ::keydown),
 
             // Disable native drag-and-drop to avoid users dragging in unsupported file formats and
@@ -50,8 +52,8 @@ class Application(
         // The various tools Phantasmal World consists of.
         val tools: List<PwTool> = listOf(
             addDisposable(Viewer(assetLoader, uiStore, createThreeRenderer)),
-            addDisposable(QuestEditor(assetLoader, uiStore, createThreeRenderer)),
-            addDisposable(HuntOptimizer(assetLoader, uiStore)),
+            addDisposable(QuestEditor(keyValueStore, assetLoader, uiStore, createThreeRenderer)),
+            addDisposable(HuntOptimizer(keyValueStore, assetLoader, uiStore)),
         )
 
         // Controllers.
diff --git a/web/src/main/kotlin/world/phantasmal/web/core/persistence/KeyValueStore.kt b/web/src/main/kotlin/world/phantasmal/web/core/persistence/KeyValueStore.kt
new file mode 100644
index 00000000..a8cc74c8
--- /dev/null
+++ b/web/src/main/kotlin/world/phantasmal/web/core/persistence/KeyValueStore.kt
@@ -0,0 +1,28 @@
+package world.phantasmal.web.core.persistence
+
+import kotlinx.browser.localStorage
+
+interface KeyValueStore {
+    suspend fun get(key: String): String?
+    suspend fun put(key: String, value: String)
+}
+
+class LocalStorageKeyValueStore : KeyValueStore {
+    override suspend fun get(key: String): String? =
+        localStorage.getItem(key)
+
+    override suspend fun put(key: String, value: String) {
+        localStorage.setItem(key, value)
+    }
+}
+
+class MemoryKeyValueStore : KeyValueStore {
+    private val map = mutableMapOf<String, String>()
+
+    override suspend fun get(key: String): String? =
+        map[key]
+
+    override suspend fun put(key: String, value: String) {
+        map[key] = value
+    }
+}
diff --git a/web/src/main/kotlin/world/phantasmal/web/core/persistence/Persister.kt b/web/src/main/kotlin/world/phantasmal/web/core/persistence/Persister.kt
index aec57117..720396e8 100644
--- a/web/src/main/kotlin/world/phantasmal/web/core/persistence/Persister.kt
+++ b/web/src/main/kotlin/world/phantasmal/web/core/persistence/Persister.kt
@@ -1,6 +1,5 @@
 package world.phantasmal.web.core.persistence
 
-import kotlinx.browser.localStorage
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.serializer
@@ -9,7 +8,7 @@ import world.phantasmal.web.core.models.Server
 
 private val logger = KotlinLogging.logger {}
 
-abstract class Persister {
+abstract class Persister(private val store: KeyValueStore) {
     private val format = Json {
         classDiscriminator = "#type"
         ignoreUnknownKeys = true
@@ -23,7 +22,7 @@ abstract class Persister {
     @Suppress("RedundantSuspendModifier")
     protected suspend fun <T> persist(key: String, data: T, serializer: KSerializer<T>) {
         try {
-            localStorage.setItem(key, format.encodeToString(serializer, data))
+            store.put(key, format.encodeToString(serializer, data))
         } catch (e: Throwable) {
             logger.error(e) { "Couldn't persist ${key}." }
         }
@@ -44,7 +43,7 @@ abstract class Persister {
     @Suppress("RedundantSuspendModifier")
     protected suspend fun <T> load(key: String, serializer: KSerializer<T>): T? =
         try {
-            val json = localStorage.getItem(key)
+            val json = store.get(key)
             json?.let { format.decodeFromString(serializer, it) }
         } catch (e: Throwable) {
             logger.error(e) { "Couldn't load ${key}." }
diff --git a/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/HuntOptimizer.kt b/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/HuntOptimizer.kt
index 14d1c4a3..e20c2d51 100644
--- a/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/HuntOptimizer.kt
+++ b/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/HuntOptimizer.kt
@@ -3,6 +3,7 @@ package world.phantasmal.web.huntOptimizer
 import world.phantasmal.web.core.PwTool
 import world.phantasmal.web.core.PwToolType
 import world.phantasmal.web.core.loading.AssetLoader
+import world.phantasmal.web.core.persistence.KeyValueStore
 import world.phantasmal.web.core.stores.ItemDropStore
 import world.phantasmal.web.core.stores.ItemTypeStore
 import world.phantasmal.web.core.stores.UiStore
@@ -16,6 +17,7 @@ import world.phantasmal.webui.DisposableContainer
 import world.phantasmal.webui.widgets.Widget
 
 class HuntOptimizer(
+    private val keyValueStore: KeyValueStore,
     private val assetLoader: AssetLoader,
     private val uiStore: UiStore,
 ) : DisposableContainer(), PwTool {
@@ -25,8 +27,8 @@ class HuntOptimizer(
         val itemTypeStore = addDisposable(ItemTypeStore(assetLoader))
 
         // Persistence
-        val huntMethodPersister = HuntMethodPersister()
-        val wantedItemPersister = WantedItemPersister(itemTypeStore)
+        val huntMethodPersister = HuntMethodPersister(keyValueStore)
+        val wantedItemPersister = WantedItemPersister(keyValueStore, itemTypeStore)
 
         // Stores
         val huntMethodStore =
diff --git a/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/persistence/HuntMethodPersister.kt b/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/persistence/HuntMethodPersister.kt
index c6251a0a..6f732b29 100644
--- a/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/persistence/HuntMethodPersister.kt
+++ b/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/persistence/HuntMethodPersister.kt
@@ -1,12 +1,13 @@
 package world.phantasmal.web.huntOptimizer.persistence
 
 import world.phantasmal.web.core.models.Server
+import world.phantasmal.web.core.persistence.KeyValueStore
 import world.phantasmal.web.core.persistence.Persister
 import world.phantasmal.web.huntOptimizer.models.HuntMethodModel
 import kotlin.time.Duration
 import kotlin.time.DurationUnit.HOURS
 
-class HuntMethodPersister : Persister() {
+class HuntMethodPersister(keyValueStore: KeyValueStore) : Persister(keyValueStore) {
     suspend fun persistMethodUserTimes(huntMethods: List<HuntMethodModel>, server: Server) {
         val userTimes = mutableMapOf<String, Double>()
 
diff --git a/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/persistence/WantedItemPersister.kt b/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/persistence/WantedItemPersister.kt
index 6cd7abba..8643866e 100644
--- a/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/persistence/WantedItemPersister.kt
+++ b/web/src/main/kotlin/world/phantasmal/web/huntOptimizer/persistence/WantedItemPersister.kt
@@ -1,12 +1,17 @@
 package world.phantasmal.web.huntOptimizer.persistence
 
 import world.phantasmal.web.core.models.Server
+import world.phantasmal.web.core.persistence.KeyValueStore
 import world.phantasmal.web.core.persistence.Persister
 import world.phantasmal.web.core.stores.ItemTypeStore
-import world.phantasmal.web.shared.dto.WantedItemDto
 import world.phantasmal.web.huntOptimizer.models.WantedItemModel
+import world.phantasmal.web.shared.dto.WantedItemDto
+
+class WantedItemPersister(
+    keyValueStore: KeyValueStore,
+    private val itemTypeStore: ItemTypeStore,
+) : Persister(keyValueStore) {
 
-class WantedItemPersister(private val itemTypeStore: ItemTypeStore) : Persister() {
     suspend fun persistWantedItems(wantedItems: List<WantedItemModel>, server: Server) {
         persistForServer(server, WANTED_ITEMS_KEY, wantedItems.map {
             WantedItemDto(it.itemType.id, it.amount.value)
diff --git a/web/src/main/kotlin/world/phantasmal/web/questEditor/QuestEditor.kt b/web/src/main/kotlin/world/phantasmal/web/questEditor/QuestEditor.kt
index 52225461..0a75e4bf 100644
--- a/web/src/main/kotlin/world/phantasmal/web/questEditor/QuestEditor.kt
+++ b/web/src/main/kotlin/world/phantasmal/web/questEditor/QuestEditor.kt
@@ -6,6 +6,7 @@ import org.w3c.dom.HTMLCanvasElement
 import world.phantasmal.web.core.PwTool
 import world.phantasmal.web.core.PwToolType
 import world.phantasmal.web.core.loading.AssetLoader
+import world.phantasmal.web.core.persistence.KeyValueStore
 import world.phantasmal.web.core.rendering.DisposableThreeRenderer
 import world.phantasmal.web.core.stores.UiStore
 import world.phantasmal.web.core.undo.UndoManager
@@ -25,6 +26,7 @@ import world.phantasmal.webui.dom.disposableListener
 import world.phantasmal.webui.widgets.Widget
 
 class QuestEditor(
+    private val keyValueStore: KeyValueStore,
     private val assetLoader: AssetLoader,
     private val uiStore: UiStore,
     private val createThreeRenderer: (HTMLCanvasElement) -> DisposableThreeRenderer,
@@ -38,7 +40,7 @@ class QuestEditor(
         val entityAssetLoader = addDisposable(EntityAssetLoader(assetLoader))
 
         // Persistence
-        val questEditorUiPersister = QuestEditorUiPersister()
+        val questEditorUiPersister = QuestEditorUiPersister(keyValueStore)
 
         // Undo
         val undoManager = UndoManager()
diff --git a/web/src/main/kotlin/world/phantasmal/web/questEditor/persistence/QuestEditorUiPersister.kt b/web/src/main/kotlin/world/phantasmal/web/questEditor/persistence/QuestEditorUiPersister.kt
index 1f23c660..09b261a2 100644
--- a/web/src/main/kotlin/world/phantasmal/web/questEditor/persistence/QuestEditorUiPersister.kt
+++ b/web/src/main/kotlin/world/phantasmal/web/questEditor/persistence/QuestEditorUiPersister.kt
@@ -1,10 +1,11 @@
 package world.phantasmal.web.questEditor.persistence
 
 import world.phantasmal.web.core.controllers.*
+import world.phantasmal.web.core.persistence.KeyValueStore
 import world.phantasmal.web.core.persistence.Persister
 import world.phantasmal.web.shared.dto.*
 
-class QuestEditorUiPersister : Persister() {
+class QuestEditorUiPersister(keyValueStore: KeyValueStore) : Persister(keyValueStore) {
     // TODO: Throttle this method.
     suspend fun persistLayoutConfig(config: DockedItem) {
         persist(LAYOUT_CONFIG_KEY, toDto(config))
diff --git a/web/src/test/kotlin/world/phantasmal/web/application/ApplicationTests.kt b/web/src/test/kotlin/world/phantasmal/web/application/ApplicationTests.kt
index a6262dac..22f0bb08 100644
--- a/web/src/test/kotlin/world/phantasmal/web/application/ApplicationTests.kt
+++ b/web/src/test/kotlin/world/phantasmal/web/application/ApplicationTests.kt
@@ -2,6 +2,7 @@ package world.phantasmal.web.application
 
 import kotlinx.browser.document
 import world.phantasmal.web.core.PwToolType
+import world.phantasmal.web.core.persistence.MemoryKeyValueStore
 import world.phantasmal.web.test.TestApplicationUrl
 import world.phantasmal.web.test.WebTestContext
 import world.phantasmal.web.test.WebTestSuite
@@ -30,8 +31,10 @@ class ApplicationTests : WebTestSuite {
 
     private fun WebTestContext.initialization_and_shutdown_succeeds(url: String) {
         components.applicationUrl = TestApplicationUrl(url)
+
         disposer.add(
             Application(
+                keyValueStore = MemoryKeyValueStore(),
                 rootElement = document.body!!,
                 assetLoader = components.assetLoader,
                 applicationUrl = components.applicationUrl,
diff --git a/web/src/test/kotlin/world/phantasmal/web/huntOptimizer/HuntOptimizerTests.kt b/web/src/test/kotlin/world/phantasmal/web/huntOptimizer/HuntOptimizerTests.kt
index e445f61a..b5c46eb3 100644
--- a/web/src/test/kotlin/world/phantasmal/web/huntOptimizer/HuntOptimizerTests.kt
+++ b/web/src/test/kotlin/world/phantasmal/web/huntOptimizer/HuntOptimizerTests.kt
@@ -1,6 +1,7 @@
 package world.phantasmal.web.huntOptimizer
 
 import world.phantasmal.web.core.PwToolType
+import world.phantasmal.web.core.persistence.MemoryKeyValueStore
 import world.phantasmal.web.test.TestApplicationUrl
 import world.phantasmal.web.test.WebTestSuite
 import kotlin.test.Test
@@ -10,7 +11,10 @@ class HuntOptimizerTests : WebTestSuite {
     fun initialization_and_shutdown_should_succeed_without_throwing() = test {
         components.applicationUrl = TestApplicationUrl("/${PwToolType.HuntOptimizer}")
 
-        val huntOptimizer = disposer.add(HuntOptimizer(components.assetLoader, components.uiStore))
+        val huntOptimizer = disposer.add(
+            HuntOptimizer(MemoryKeyValueStore(), components.assetLoader, components.uiStore)
+        )
+
         disposer.add(huntOptimizer.initialize())
     }
 }
diff --git a/web/src/test/kotlin/world/phantasmal/web/questEditor/QuestEditorTests.kt b/web/src/test/kotlin/world/phantasmal/web/questEditor/QuestEditorTests.kt
index 1a1e3f76..52238fe7 100644
--- a/web/src/test/kotlin/world/phantasmal/web/questEditor/QuestEditorTests.kt
+++ b/web/src/test/kotlin/world/phantasmal/web/questEditor/QuestEditorTests.kt
@@ -1,6 +1,7 @@
 package world.phantasmal.web.questEditor
 
 import world.phantasmal.web.core.PwToolType
+import world.phantasmal.web.core.persistence.MemoryKeyValueStore
 import world.phantasmal.web.test.TestApplicationUrl
 import world.phantasmal.web.test.WebTestSuite
 import kotlin.test.Test
@@ -11,8 +12,14 @@ class QuestEditorTests : WebTestSuite {
         components.applicationUrl = TestApplicationUrl("/${PwToolType.QuestEditor}")
 
         val questEditor = disposer.add(
-            QuestEditor(components.assetLoader, components.uiStore, components.createThreeRenderer)
+            QuestEditor(
+                MemoryKeyValueStore(),
+                components.assetLoader,
+                components.uiStore,
+                components.createThreeRenderer,
+            )
         )
+
         disposer.add(questEditor.initialize())
     }
 }
diff --git a/web/src/test/kotlin/world/phantasmal/web/viewer/ViewerTests.kt b/web/src/test/kotlin/world/phantasmal/web/viewer/ViewerTests.kt
index 2781deda..b7a99473 100644
--- a/web/src/test/kotlin/world/phantasmal/web/viewer/ViewerTests.kt
+++ b/web/src/test/kotlin/world/phantasmal/web/viewer/ViewerTests.kt
@@ -13,6 +13,7 @@ class ViewerTests : WebTestSuite {
         val viewer = disposer.add(
             Viewer(components.assetLoader, components.uiStore, components.createThreeRenderer)
         )
+
         disposer.add(viewer.initialize())
     }
 }