I often hear that the success of the Firefox web browser is largely due to its open plug in architecture. I also hear that you should limit the number of plug ins you use, since they slow down FF and cause it to crash. I’m currently using 4 plug ins – AdBlock Plus, AVG Safe Search, Firebug, and Xmarks.
I don’t really know what AdBlock does, other than what I can gather from the name.
I’ll probably be removing AVG soon because I’m thinking of switching to Microsoft Security Essentials on my Windows machines.
I used Firebug once.
I like the Xmarks password syncing, but I’m not a big bookmarker. I don’t think anyone really uses bookmarks.
I don’t seem to need plug ins at all.