Amit at digital inspiration wrote 2 tips on improving Firefox's browsing speed, according to him, those tips will make your firefox faster so it will deliver the better browsing experience.
The first tips is making a new profile without any modifications and runs firefox with the new profiles. If you need some bookmarks from your old profile, you can import first from your previous profile. LOL .. I tried this tips and I was surprised, it runs just like a fresh installation of firefox.
The second tips, is an alternative trick from James Meyer, by copying the firefox's preference file (prefs.js) and edit the file. Eliminate the lines that are related to various add-ons. This sound more complicated from the first tips, and haven't tried this, according to James, you have to make the prefs.js backed up first before deleting any lines.
You can read those tips on digital inspiration as well as any other useful tips.