diff --git a/CHANGES.md b/CHANGES.md
index 2357a0a..80501be 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## v4.2.1
+
+- Fix browser check
+
 ## 4.2.0
 
 - Port to TypeScript
diff --git a/package.json b/package.json
index ff99de6..81e30a3 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "reverse-image-search",
   "description": "Reverse Image Search",
-  "version": "4.2.0",
+  "version": "4.2.1",
   "author": "Brawl345",
   "license": "Unlicense",
   "repository": {
diff --git a/public/manifest.json b/public/manifest.json
index 2389a83..d0a73ef 100644
--- a/public/manifest.json
+++ b/public/manifest.json
@@ -4,7 +4,7 @@
   "name": "__MSG_extensionName__",
   "description": "__MSG_extensionDescription__",
   "author": "Andreas Bielawski",
-  "version": "4.2.0",
+  "version": "4.2.1",
   "icons": {
     "16": "icons/16.png",
     "32": "icons/32.png",
diff --git a/source/options/components/Provider.svelte b/source/options/components/Provider.svelte
index 8cd2446..a8f44e0 100644
--- a/source/options/components/Provider.svelte
+++ b/source/options/components/Provider.svelte
@@ -23,7 +23,7 @@
   $: iconUrl = getIcon(provider.icon);
 
   const uploadIcon = () => {
-    if (isFirefox) {
+    if (!isFirefox) {
       errorMsg = getMessage("msgIconUploadNotSupported");
       return;
     }
diff --git a/source/utils.ts b/source/utils.ts
index 9105a04..6d85ab9 100644
--- a/source/utils.ts
+++ b/source/utils.ts
@@ -50,5 +50,6 @@ export const base64EncodeIcon = (ctx: CanvasRenderingContext2D): string => {
   return jpegBase64;
 };
 
-// @ts-ignore
-export const isFirefox = window.browser && browser.runtime;
+export const isFirefox =
+  // @ts-ignore
+  typeof window !== 'undefined' && window.browser && browser.runtime;