Some firefox extensions I use (i'm unsure if they'll actually speed things up but it'll make life easier) :
AdBlock - An ad blocker plugin for Firefox. Easy to use and learn.
(if you want a useful filter list let me know)
ChatZilla - IRC client for Firefox.
Download Manager Tweak - Improves Firefox's built-in download manager.
Download Statusbar - Monitor your downloads in the Firefox statusbar.
FirefoxView - If for some reason you started your internet session in Internet Exploiter, you can right click anywhere on the page and click a new menu option to open the same page in Firefox.
FireFTP - A simple, easy-to-use, graphical FTP client for Firefox.
FlashGot - Enables Firefox interaction with several popular download managers, such as FlashGet and GetRight.
GMail Notifier - Check your GMail inbox from your Firefox statusbar.
GoogleBar - An unofficial Firefox version of the critically acclaimed Google Toolbar for IE. Includes all the functionalities its IE counterpart has, and then some more.
Hotmail Tabs - For some reason, Hotmail's sourcecode was changed and now it manages internal navigation through Javascript (which normally doesn't allow tabbed navigation). This extension allows you to navigate your Hotmail account in several tabs.
jsLib - Firefox's Javascript library.
OpenNewWindowFromHere - Allows you to right click a page and open a new tab/window from that URL location.
Secure Password Generator - An eccentric extension, it helps you generate secure passwords for your protected stuff (email accounts, documents, forum accounts, etc.).