First off, use the middle mouse button to click a link, or (ctrl+left mouse), Tabbed Browsing

(the most usefull feature in the world, one that just about every browser EXCEPT IE has)
Second, goto any website with popups, THERE ARE NONE! (you can manually put sites on your allow list if you need to, like ICQ anywhere, etc...).
Third, find an ad or images from any server (like big ugly sig images) right click on the image and "block images from this server!" (i've done this to 100+ servers so far)
Fourth I would check all of the addons and plugins available.
The main features of firefox are under the hood, so its not really visual things, just great security (you will never have your browser hijacked, or your homepage forcefully changed, porn links forcefully installed on your PC and favorites, viri installed on your PC by your browser, (or any other internet crap like that that goes on)) (and all of this is Out Of The Box, no 3rd party anything) All of it is easily configureable as well.
Just try not to use its downloader too often, its buggy.
Odd, I have downloaded thousands of files with the downloader (file sizes ranging from 5K to 600 MB), and I love it, perfect files everytime, pause/resume functions, all of the downloads on one dialog, etc.. its great. There are even really great plugins for the downloader.