Is Firefox in Full Screen mode by accident? (Try pressing F11 to turn Full Screen on or off.) Does this still happen if you restart with add-ons disabled?

For some other possible solutions, see this article: Navigation buttons like back, home, bookmarks and reload are missing

Try a different theme in Linux and also check the Controls and Icons.

• GNOME > Look and Feel > Appearance > Theme

It's not in full screen, as the window border and toolbars are there. I don't have any addons installed, except the ubuntu modifications one, which is disabled. The buttons themselves aren't quite missing, they're just not visible, they are a few pixels wide each, and they have no icon, they do highlight on mouseover, and they still respond to clicks... I can see only two buttons, the bookmarks button and the reload button.

I started firefox in safe mode, reset the toolbars to defaults, but still no icons, I can see the buttons if I enable "text only" in the customisation window, but I'd rather have the icons.

Changing my theme fixes radio buttons and buttons in webpages, but the buttons on the toolbar are still missing(I suspect I have two different problems), and I want to use my preffered theme. There's nothing wrong with my gnome theme, as no other programs (GIMP, Google Chrome, firefox 6.0) have this problem when using it.

This seems to only be a problem when downloading firefox from the site. After the ppa got updated, it works fine..