I use Firefox 3.5.3 on Windows 7 RTM, I open about 20 tabs (as my home page(s)) and I have 45 add-ins that do everything from block advertisements to open Internet Explorer tabs. I have Windows 7 64-bit RTM with 8 GB of RAM (please refer to other questions/answers about how much of this is usable). What is your best suggestion for speeding it up?
The obvious one is to uninstall add ons that are not needed, but if you need all of them, then obviously you can't.
The are not really many things you can do other than go to about:config and tinker with various settings.
Recently, one of The Firefox developers talked about a method of clearing the SQLite database in order to speed it up slightly.
In addition, if you are feeling that flash is very jumpy, there is a article on how to fix that.
Again, if you are seeing a lot of speed problems, it is probably due to just having so many addons... Even if separately the addons works well, I have noticed that you can have a big exponential increase in delays/lag when some are combined.
What kind of speed up are you looking for? Is there anything that is particularly slow?
In general, if you really want to make things go faster, the first thing I would look to do is decrease the number of add-on installed. That can make an incredible difference. If some of the add-ons are used only on occasion or for a particular purpose, consider setting up alternate profiles just for those extensions so they're not loaded for general browsing.
Maybe some little tweaks will also help you:
Explanation for the "network.http.pipelining"-settings: pipelining reduces network load and can reduce page loading times over high-latency connections, but not all servers support it. Some servers may even behave incorrectly if they receive pipelined requests. Personally - until now - I had never problems with this settings.
These settings should give you more performance in opening web-sites and in browsing the Internet.