Switch to working Firefox download badge icon

Author: rugk

README.md

@@ -17,7 +17,7 @@ It is inspired by [the old Offline QR code generator add-on](https://github.com/
 
 ## Download
 
-**[![Get it for Firefox!](https://addons.cdn.mozilla.net/static/img/addons-buttons/AMO-button_1.png)](https://addons.mozilla.org/firefox/addon/offline-qr-code-generator/?utm_source=github.com&utm_medium=git&utm_content=download-button&utm_campaign=github)**
+**[![Get it for Firefox!](https://extensionworkshop.com/assets/img/documentation/publish/get-the-addon-178x60px.dad84b42.png)](https://addons.mozilla.org/firefox/addon/offline-qr-code-generator/?utm_source=github.com&utm_medium=git&utm_content=download-button&utm_campaign=github)**
 
 > **BTW:** If you want to search and insert emojis easily on all your websites, do check out our **[Awesome Emoji Picker](https://github.com/rugk/awesome-emoji-picker/?utm_source=github.com&utm_medium=git&utm_content=download-button&&utm_campaign=github-btw-do-you-also-know-readme)** too!