The complete list is available on Mozillazine page
The ones I use all the time:
- about:robots and about:mozilla. Not really useful, but I’ve got to start from those.
- about:config – Firefox settings and tweaks
- about:cache – Shows memory, disk and offline cache parameters. To get details and list of pages in each cache (from where there’s access to detailed information on each page):
- about:plugins – list of installed plug-ins