Here’s what my Firefox browser looks like on my home PC, showing four add-ons I think are essential:

• Foxmarks – I dithered about adding this for a few weeks but now I have it installed on my home PC, work PC, and EeePC. Foxmarks syncs and backs up your bookmarks across multiple computers, so I now never need to worry about losing a bookmark or being on the wrong PC. Best thing is you can set up different profiles e.g. oneset of bookmarks for work and another for home.
• Greasemonkey – This lets you install scripts that overlay or modify webpages. I had this installed before but didn’t really use it; I’ve reinstalled it now though to make use of an excellent script that ties Last.fm to Spotify. Band names and tracks now have a little green note next to them on Last.fm – clicking on the note opens a search in Spotify:

• MyScrobble – Made for Last.fm Hack Day 2008, the Universal Scrobbler scrobbles the unscrobbable: for example tracks from a band’s MySpace page.
• Twitterfox -One of several Twitter add-ons, Twitterfox checks you twitter feed every X minutes and notifies you of any new tweets (much like the Gmail plugin). You can then click the little blue t to open a window to read adn reply to your tweets. It’s quite unobtrusive and much more SFW than visiting Twitter pages directly: