I know many people who use Mozilla or Firefox also use the Adblock extension. It's awesome. I have noticed something that it is important to be aware of - especially for newer users. There are some pages which, when adblock is enabled and told to "remove ads," do not render correctly.
This is not a Mozilla rendering problem. This is specifically because of the adblock extension. The pages are intentionally designed to misplace a horizontal menu over the main text of the page when the ads are removed. If you have the adblock extension and it is set to "remove ads," you can see what I'm talkin about at
www.wheresgeorge.com and also <a href="http://www.nydailynews.com/news/gossip/story/262317p-224624c.html">this news site</a>. To fix this, all one needs to do is set adblock to only "hide ads" instead of remove them. I do it only temporarily when I come across a site like this, but you could also leave it that way all the time if you would prefer it that way.