better testing instructions

README.md

@@ -54,7 +54,10 @@ A green checkmark will appear next to the *Save* button if your connection is wo
 - **Autostart**: Autostart and prioritize videos send from this extension.
 
 ## Test this extension
-Use the correct manifest file for your browser. Either rename the browser specific file to `manifest.json` before loading the addon or symlink it to the correct location, e.g. `ln -s manifest-firefox.json manifest.json`.
+Before continuing loading the temporary extension here, make sure to deactivate/delete the main extension first.
+
+Symlink/copy the correct manifest file for your browser to the expected location, e.g. `ln -s manifest-firefox.json manifest.json`.
+
 - Firefox
   - Open `about:debugging#/runtime/this-firefox`
   - Click on *Load Temporary Add-on*