I installed Firefox 19. Immediately most of my add ons stopped working, and in some cases work but not correctly.
Here are some examples:
Noia4 - works, but each time I restart Firefox Noia4 reset to default settings.
Reminder Fox - Does not work
Status4Evar - Does not work - These may be related.
Google translator for Firefox, does not work.
AnonymoX does not work.
I have not had time to try ALL my add ons, so until I can be sure these work correctly I have returned to v18.
If you see disabled, not compatible, extensions in "Tools > Add-ons > Extensions" then click the Tools button at the left side of the Search Bar (or click the "Find Updates" button in older Firefox versions) to check if there is a compatibility update available.
If this hasn't helped then also try to delete the addons.sqlite file.