To install Firebug manually you have to do it differently. There are two ways to run extensions manually:
1. Extract the XPI
- Download the XPI file that contains the extension
- Locate the ‘extensions’ folder within your profile (e.g. via Firefox menu > Help > Troubleshooting Information > Show Folder)
- Create a new folder within the ‘extensions’ folder and call it like the add-on’s id (for Firebug this is
- Extract the XPI into that folder
2. Get the sources from the git repository
A detailed description for how to do that can be found on the development setup description on the Firebug wiki. It’s similar to the description above with the addition that you’ll be able to always get the latest sources.