I still use Internet Explorer to read my Outlook Webmail from home as - suspiciously - this Microsoft product only works properly with the Microsoft reader.
The major Firefox extensions I use are:
- Colourful tabs - which makes each tab display in a different colour
- Del.icio.us toolbar - lets me tag things instantly for upload to del.icio.us
- Evernote web clipper - lets me upload almost anything as a "note" in my private notes database
- Greasemonkey - allows me to run a number of little useful scripts that do other things
- Meebo - instant messaging
- OpenURL referrer - from OCLC - I was fiddling with it for the Web Presence project
- Remember the Milk for gmail - puts a "to do" list into my gmail account
- Ubiquity - I press [CTRL] [SPACE] and a command line appears, allowing me to just type a command and look up something on wikipedia or sent a message to twitter or something to gmail, all from one spot
- Zotero - see Thing 8