I've installed it on my n900, but it's unusably slow, especially compared to MicroB, which is the default browser on Maemo (which also uses the gecko engine). It takes ages to start up, uses up all the CPU, and it takes 5 minutes before you finally managed to load a page. Also, after you close the browser, there's a 'fennec' process still using all the CPU cycles and draining your battery.
Too bad, because I do like its feature set: Firefox sync, addons, etc, but I'll stick to MicroB until they find a solution to the CPU use issue.