Back/Forward Dropdown Remover is a tiny extension that removes the dropdown arrows from Firefox's Back and Forward buttons.
This add-on is no longer being updated (by me)—there won't be an update compatible with Firefox 3 (or later versions).
It's now compatible with Firefox 0.9.x and 1.0.x, as well as “Deer Park” development versions and Firefox 1.5 beta onwards. I figured out compatibility with 1.0.x, despite it requiring a more complex, obsolete extension packaging system, mainly because lots of people couldn't read
Requires: Firefox: Deer Park - Deer Park.
The userChrome CSS code itself has been floating around for ages on various Firefox tips sites; I just packaged it up into an extension for ease of installation, and in order to gain some limited extension-making mojo.