docs: update README.md

README.md

@@ -10,18 +10,28 @@ Get the extension on the [Chrome Web Store](https://chrome.google.com/webstore/d
 
 Get the extension on the [Firefox Browser Add-ons](https://addons.mozilla.org/en-US/firefox/addon/forks-diff-counter-for-github/).
 
-### Unpacked
+## Contributing
 
-#### Google Chrome
+Clone the repo with `git clone https://github.com/giacomoferretti/forks-diff`
 
-1. Download the repo by using `git clone https://github.com/giacomoferretti/forks-diff`
-2. Visit `chrome://extensions/` in Google Chrome
-3. Enable "Developer mode"
-4. Click on "Load unpacked"
-5. Select the cloned folder
+### Google Chrome
+
+1. Visit `chrome://extensions/`
+2. Enable "Developer mode"
+3. Click on "Load unpacked"
+4. Select the cloned folder
+
+When updating the plugin, remember to reload it.
+
+### Mozilla Firefox
+
+1. Changed `manifest_version` inside `manifest.json` from `3` to `2`
+2. Visit `about:debugging#/runtime/this-firefox`
+3. Under "Temporary Extensions" click on "Load Temporary Add-on..."
+4. Select `manifest.json`
 
 When updating the plugin, remember to reload it.
 
-## How to pack
+### How to pack
 
 Use the `pack.sh` script to generate the zip file.