Some crazy guy decided to install the 100 most popular Firefox extensions. Looks like Opera 
The 100th extension he installed was the XPI Install Delay Remover, which would have saved tons of time if it was installed first (probably at least 10 minutes)
It is quite amazing the browser manages to be stable and not too slow. Quite a few of the popular extensions used to have memory leaks (and extensions are a big cause of Firefox memory leaks). I seem to remember the Mozilla putting an emphisis on reducing memory leaks in extensions recently, so it may have worked quite well.
I know someone with about 50 extensions so perhaps it's not so surprising all 100 installed without any hiccups.
Just 6 extensions here – Evolution Toolbar, Sage, Web Developer Toolbar, Live HTTP Headers, DOM Inspector and Customize Google.