Emboldened by my success with optimized Windows builds the other day, I had a go with a Linux version this weekend. I chose Swiftfox 1.8, which is just a regular rebuild of the standard release for various different architectures. It was simple enough to extract the archive and set up a shortcut, it did seem to be a good deal swifter on my Pentium III laptop. The only problem I encountered was that my Pinball theme wasn't working, and neither were any of my extensions. They were all listed in the Themes and Extensions windows respectively, but Swiftfox behaved as if they weren't there. Uninstalling and re-installing didn't seem to have any effect either. In the end I had to create a new profile from scratch (after backing up my current one, of course), after that themes and extensions installed and worked fine, and the whole thing is noticeably faster than vanilla Firefox.