This forum is one that might start fistfights in the Blogger Cafe . . . so handle with care. If you could ONLY recommend TWO of your very favorite extensions, which two would you nominate?
Delicious Bookmarks (version 2): Even without the social network/sharing aspects of del.icio.us, which are great, using this plug-in makes it easier for me to organize and search my own bookmarks than the built-in features of any browser I've used. Plus my bookmarks easily follow me to any computer I use.
Google Gears: Allows offline access to Google docs (word processing) and Google spreadsheets even when I don't have an internet connection. Docs can be edited while offline. Spreadsheet is only read-only for now.
Unplug was a favorite until I discovered that I couldn't download much-coveted videos from theonion.com. So I switched to videodownloadhelper and never looked back.
I am making note of each the choices made here to add them to my Firefox and experiment later. BTW: I run my Firefox application entirely from my flash drive with a very cool application called Portable Apps. Running Firefox this way, I have all of my settings, tool bars, extensions, add-ons, etc. with me on any computer that I may use! Give it a try...
As for my two favorite extensions, I couldn't live without GButts, which gives quick access to GMail, Google Calendar, Google Docs, Google Maps, etc., and QuickNote, giving me an easy method of taking notes and copying text from websites.
But I would also recommend exploring the Dictionary Tooltip, which lets you double click on any word on any webpage to get a dictionary pop-up (and audio), and the Text Size Toolbar, which lets me enlarge the text on a website when I am using a projector.
I'm also currently experimenting with FireShot, which gives me the ability for screen (and partial screen) captures...
I second this! Foxmarks is great! No more, "Oh I must have saved that bookmark on my other comptuer." PicLens is the coolest. Showing my non-tech friends piclens is how I usually convince them to start using firefox.