I use the Firefox default theme but have modified it a little. In the
Tips & Tricks page under the 'Browser Appearance' heading, there two options I use.
1. Change the width of the Search Bar (the built-in Google search entry box). This because the default width is a bit too narrow for me.
2. Use your own background image for the toolbars. I created a small graphic that has alternate light and mid-grey stripes. With the script and instructions provided by Firefox, the graphic makes the toolbars appear as shown (follow the link in my post above).
Also, I don't like too much of the screen being taken up with toolbars, so the bookmarks from the 'Bookmarks Toolbar' have been moved to the empty space next to the File, Edit, Help menus. The Bookmarks Toolbar can then be switched off, so providing more screen space for web pages.
There will always be differing opinions on which browser is faster. Firefox pretty good as regards speed. Opera is fast too but with my liking for minimal toolbars, I find it slightly annoying that the space next to the File, Edit, Help menus is not available for favourite bookmarks. Another slight annoyance is that the text on the FunTrivia Forum Index displays centred instead of on the left as other browsers show it. All trivial I know but it's enough to tip the balance in Firefox's favour for me.
Avant, MyIE2, and SlimBrowser all use IE as their engine rather than them being stand-alone browsers. They add a number of enhancements such as: some security measures, tabbed browsing and a new visual look. Basically though, they are Internet Explorer under the bonnet (hood).
Edit: typo