There is a relatively easy fix. With Firefox closed go to your profile directory. From that directory, delete the following files (if they exits):
- extensions.ini
- extensions.cache
- extensions.rdf
- extensions.sqlite
- extensions.sqlite-journal
When Firefox is next started, all the files will be rebuilt from scratch.
This should eliminate the "Extension data is still loading ... " problem. If it does not, please start of new thread so we may debug it.