I stumbled across an open-source version of Firefox, called "Palemoon" which I downloaded from my usual trusted site, the Internode "Majorgeeks" software mirror.
Palemoon is a carbon copy of Firefox, but is claimed to run 25% faster due to having the Linux and Mac code exorcised and the Win 7 code optimised. Believe it or not......
Anyway, I've been running it now for a week or so and it's certainly much faster and is totally visually and user - identical to the normal Firefox releases, and just as stable. Runs all my add-ons. It does not overwrite Firefox, so you can compare both for speed. My wife didn't even know I'd changed until I told her.
Worth a try if you like snappy screen operation.
Here's their website:
http://www.palemoon.org/