I've been running Firefox for a while, and I've found some pretty good apps, especially two. the first one i recommend is Ad Block plus, this app blocks any banners from showing on any website, great way to speed up browsing a little.
Another one that i use, since i am a download fanatic, is Down it All This is a great download organizer/accelerator. it accelerates download speeds 4X faster. and allows you to rename the file, choose the destination folder and so on.
One of my favorite things to do with Firefox is to pipeline it. At default, Firefox is set to load objects on a web page one object at a time, by pipelining it, you can extend it to load about 8 objects at a time, speeding it up pretty effectively. To do this, type in "about:config" into your the web browser. Ignore the message that comes up, type in "pipe" into the filter bar. change the first and last value to true. and set the maxrequest number to 8.
NOTE- you can set the maxrequest number up to 16, but any faster than that could cause your Firefox to crash. Thanks for reading
message me if you need help.
(edit) Thanks drumfreak for your recommendation on cooliris, seems helpful for those who are streaming lots of multimedia.