diff --git a/public/lib/eventemitter.js b/public/lib/eventemitter.js
index 51ac4eca3..abf2b8dbc 100644
--- a/public/lib/eventemitter.js
+++ b/public/lib/eventemitter.js
@@ -95,13 +95,14 @@ EventEmitter.prototype.removeListener = function (event, listener) {
 };
 
 EventEmitter.prototype.emit = async function (event) {
+    let args = [].slice.call(arguments, 1);
     if (localStorage.getItem('eventTracing') === 'true') {
         console.trace('Event emitted: ' + event, args);
     } else {
         console.debug('Event emitted: ' + event);
     }
 
-    var i, listeners, length, args = [].slice.call(arguments, 1);
+    let i, listeners, length;
 
     if (typeof this.events[event] === 'object') {
         listeners = this.events[event].slice();
@@ -120,13 +121,14 @@ EventEmitter.prototype.emit = async function (event) {
 };
 
 EventEmitter.prototype.emitAndWait = function (event) {
+    let args = [].slice.call(arguments, 1);
     if (localStorage.getItem('eventTracing') === 'true') {
         console.trace('Event emitted: ' + event, args);
     } else {
         console.debug('Event emitted: ' + event);
     }
 
-    var i, listeners, length, args = [].slice.call(arguments, 1);
+    let i, listeners, length;
 
     if (typeof this.events[event] === 'object') {
         listeners = this.events[event].slice();
diff --git a/public/scripts/extensions/expressions/index.js b/public/scripts/extensions/expressions/index.js
index e31807893..e5ba1ed21 100644
--- a/public/scripts/extensions/expressions/index.js
+++ b/public/scripts/extensions/expressions/index.js
@@ -14,7 +14,6 @@ import { ARGUMENT_TYPE, SlashCommandArgument, SlashCommandNamedArgument } from '
 import { SlashCommandEnumValue, enumTypes } from '../../slash-commands/SlashCommandEnumValue.js';
 import { commonEnumProviders } from '../../slash-commands/SlashCommandCommonEnumsProvider.js';
 import { slashCommandReturnHelper } from '../../slash-commands/SlashCommandReturnHelper.js';
-import { SlashCommandClosure } from '../../slash-commands/SlashCommandClosure.js';
 import { generateWebLlmChatPrompt, isWebLlmSupported } from '../shared.js';
 export { MODULE_NAME };
 
@@ -986,6 +985,71 @@ async function setSpriteSlashCommand(_, spriteId) {
     return label;
 }
 
+/**
+ * Returns the sprite folder name (including override) for a character.
+ * @param {object} char Character object
+ * @param {string} char.avatar Avatar filename with extension
+ * @returns {string} Sprite folder name
+ * @throws {Error} If character not found or avatar not set
+ */
+function spriteFolderNameFromCharacter(char) {
+    const avatarFileName = char.avatar.replace(/\.[^/.]+$/, '');
+    const expressionOverride = extension_settings.expressionOverrides.find(e => e.name === avatarFileName);
+    return expressionOverride?.path ? expressionOverride.path : avatarFileName;
+}
+
+/**
+ * Slash command callback for /uploadsprite
+ *
+ * label= is required
+ * if name= is provided, it will be used as a findChar lookup
+ * if name= is not provided, the last character's name will be used
+ * if folder= is a full path, it will be used as the folder
+ * if folder= is a partial path, it will be appended to the character's name
+ * if folder= is not provided, the character's override folder will be used, if set
+ *
+ * @param {object} args
+ * @param {string} args.name Character name or avatar key, passed through findChar
+ * @param {string} args.label Expression label
+ * @param {string} args.folder Sprite folder path, processed using backslash rules
+ * @param {string} imageUrl Image URI to fetch and upload
+ * @returns {Promise<void>}
+ */
+async function uploadSpriteCommand({ name, label, folder }, imageUrl) {
+    if (!imageUrl) throw new Error('Image URL is required');
+    if (!label || typeof label !== 'string') throw new Error('Expression label is required');
+
+    label = label.replace(/[^a-z]/gi, '').toLowerCase().trim();
+    if (!label) throw new Error('Expression label must contain at least one letter');
+
+    name = name || getLastCharacterMessage().original_avatar || getLastCharacterMessage().name;
+    const char = findChar({ name });
+
+    if (!folder) {
+        folder = spriteFolderNameFromCharacter(char);
+    } else if (folder.startsWith('/') || folder.startsWith('\\')) {
+        const subfolder = folder.slice(1);
+        folder = `${char.name}/${subfolder}`;
+    }
+
+    try {
+        const response = await fetch(imageUrl);
+        const blob = await response.blob();
+        const file = new File([blob], 'image.png', { type: 'image/png' });
+
+        const formData = new FormData();
+        formData.append('name', folder); // this is the folder or character name
+        formData.append('label', label); // this is the expression label
+        formData.append('avatar', file);  // this is the image file
+
+        await handleFileUpload('/api/sprites/upload', formData);
+        console.debug(`[${MODULE_NAME}] Upload of ${imageUrl} completed for ${name} with label ${label}`);
+    } catch (error) {
+        console.error(`[${MODULE_NAME}] Error uploading file:`, error);
+        throw error;
+    }
+}
+
 /**
  * Processes the classification text to reduce the amount of text sent to the API.
  * Quotes and asterisks are to be removed. If the text is less than 300 characters, it is returned as is.
@@ -1283,8 +1347,6 @@ async function drawSpritesList(character, labels, sprites) {
  * @returns {Promise<string>} Rendered list item template
  */
 async function getListItem(item, imageSrc, textClass, isCustom) {
-    const isFirefox = navigator.userAgent.toLowerCase().indexOf('firefox') > -1;
-    imageSrc = isFirefox ? `${imageSrc}?t=${Date.now()}` : imageSrc;
     return renderExtensionTemplateAsync(MODULE_NAME, 'list-item', { item, imageSrc, textClass, isCustom });
 }
 
@@ -2217,4 +2279,43 @@ function migrateSettings() {
             </div>
         `,
     }));
+    SlashCommandParser.addCommandObject(SlashCommand.fromProps({
+        name: 'uploadsprite',
+        callback: async (args, url) => {
+            await uploadSpriteCommand(args, url);
+            return '';
+        },
+        unnamedArgumentList: [
+            SlashCommandArgument.fromProps({
+                description: 'URL of the image to upload',
+                typeList: [ARGUMENT_TYPE.STRING],
+                isRequired: true,
+            }),
+        ],
+        namedArgumentList: [
+            SlashCommandNamedArgument.fromProps({
+                name: 'name',
+                description: 'Character name or avatar key (default is current character)',
+                typeList: [ARGUMENT_TYPE.STRING],
+                isRequired: false,
+                acceptsMultiple: false,
+            }),
+            SlashCommandNamedArgument.fromProps({
+                name: 'label',
+                description: 'Sprite label/expression name',
+                typeList: [ARGUMENT_TYPE.STRING],
+                enumProvider: localEnumProviders.expressions,
+                isRequired: true,
+                acceptsMultiple: false,
+            }),
+            SlashCommandNamedArgument.fromProps({
+                name: 'folder',
+                description: 'Override folder to upload into',
+                typeList: [ARGUMENT_TYPE.STRING],
+                isRequired: false,
+                acceptsMultiple: false,
+            }),
+        ],
+        helpString: '<div>Upload a sprite from a URL.</div><div>Example:</div><pre><code>/uploadsprite name=Seraphina label=joy /user/images/Seraphina/Seraphina_2024-12-22@12h37m57s.png</code></pre>',
+    }));
 })();
diff --git a/src/endpoints/sprites.js b/src/endpoints/sprites.js
index 733b12478..6a2e5e6b9 100644
--- a/src/endpoints/sprites.js
+++ b/src/endpoints/sprites.js
@@ -124,9 +124,10 @@ router.get('/get', jsonParser, function (request, response) {
                 })
                 .map((file) => {
                     const pathToSprite = path.join(spritesPath, file);
+                    const mtime = fs.statSync(pathToSprite).mtime?.toISOString().replace(/[^0-9]/g, '').slice(0, 14);
                     return {
                         label: path.parse(pathToSprite).name.toLowerCase(),
-                        path: `/characters/${name}/${file}`,
+                        path: `/characters/${name}/${file}` + (mtime ? `?t=${mtime}` : ''),
                     };
                 });
         }