There is MiniMo (Firefox is based on Mozilla) but it's not quite there yet in terms of features.

Here's the empty Garage page: https://garage.maemo.org/projects/minimo-maemo/

Here is the website of the guy porting it: http://tonikitoo.blogspot.com/search?q=minimo

Edit:
Ok, I tried to install the package minimo_0.16.8-2 and it depends on libxt6_0.1.5-2 which is incompatible w/ the N800. I haven't really put more than a couple minutes into this so it may work with an upgraded libxt6 that is floating around but a google search doesn't pull up anything worthwhile but I did see reports that it was running on the N800.