The basics: if you have Firefox you need Adblock, and if you have Adblock, you need to install the latest Filterset.G regularly. If you have Firefox and you use Smart Keywords, you need to install SmartSearch so that you can highlight something on a web page and right click it and run one of your Smart Keywords searches (I have one set up for a version of WorldCat that we have in the state of Texas and another one for our SIRSI catalog search).
Now for the beyond-the-basics suggestion... Yah, I know the choice of Firefox extensions is a highly personal decision, but if you like to try out extensions let me recommend Mouseless Browsing.
After it is installed, every page you surf to gets modified with numbers next to each hyperlink. I set my options so that I just type the number and it goes to that link (just check the time option so you don't have to press enter).
I use the numbers above the letters because I memorized them back in middle school typing in old Atari 800 BASIC programs from Antic and Analog magazines, but you can just as well use the number pad if you like.
If you find that nothing happens after you install until you hold down CTRL and press the numbers, then you probably have some other extension that conflicts.