When i first got my n800 i saw there was a Dl for firefox and since i was familiar with firefox, why not Dl it ?, couple months went by and i went on utube, and it says i need to upgrade my flash, i went to the website where i got it from "http://browser.garage.maemo.org/" and it says to go to application manager and just update "MICROB" and which, i dont have and i cant find micro B, i tried reinstalling it and the error i got was "unable to install microb-browser imcompatiable application package"

How do i reset EVERYTHING back to normal? even when i upgraded to the new diablo OS or w.e i still have this firefox installed into the nokia, how do i remove it? i feel like i wasted all my money buying the nokia n800 because of this "firefox" issue, i cant update the flash to it, please help me some one

Please see the wiki article, "Updating the tablet firmware".

If all your previous upgrades have been via Seamless Software Updates (SSU), rather than reflashing, then all your applications and settings would be kept across updates. Flashing will wipe out all add-on applications and reset all settings.

There have been a few browsers on the tablets that have been based upon core parts of Firefox, and I'm not sure which one you have installed. Regardless though, have you tried uninstalling it via the Application manager? If so, and the attempt failed, what was the error?