Back in November, I started using Firefox and I really like it. Granted, there are a few things of which I'm not very fond:

In order to move the tabs to the bottom (top is the default) you have to install an Add-On. No add-on needed for Avant Browser.

One cool thing about AB is that you can re-size tab windows within the browser window. If you have several tabs open, but you want to view only of them side-by-side, you can. This is not possible with Firefox. I found a couple add-ons, but they only let you cascade or tile ALL of your open tabs. I haven't looked for any new add-ons lately though. But then again, I really don't need that feature all that much.

And, I really can't think of anything else right now so, for the most part, it's a great browser. (ETA:) There is something that Firefox has that isn't (or at least wasn't) available with Avant Browser - re-opening closed tabs. If you accidentally close a tab, you can re-open with a single click or you can get a drop-down list of all of the recently closed tabs. (Recently, as in within the current browser session)

I did, however recently notice something a little....... odd. Firefox has this cool feature called "Instant Web Site ID" You can click on a site's "favicon" (an icon next to the site's URL in the address window of the browser) for an instant identity overview. The odd thing is, when you're on the Mozilla/Firefox site, all you get from their "favicon" is "This web site does not supply identity information. Your connection to this web site is not encrypted."