Could you give me exact steps to reproduce your problem (assuming an up-to-date Tor Browser)?
Yes. Sorry for not mentioning that you'll need the Vimperator (or Pentadactyl) extension to do this, but it used to be that you could hide the "Navigation Toolbar" from the View->Toolbars menu. Now the geniuses at Mozilla have removed that option.
Anyway. Customize toolbars to move the Torbutton on a different toolbar, for example Vimperator's status bar on the bottom. Now hide the navigation bar by entering
:set gui=nonavigation
in Vimperator's status line (hit Esc first if not in command mode). The Navigation Bar is hidden and the Torbutton won't work. Now try
:set gui+=navigation
the Navigation Bar is shown and the Torbutton will work again.
There are probably other extensions or undocumented ways to hide the Navigation Toolbar. I'm almost sure the Torbutton won't work even when the bar is hidden via other means: In other words, I really don't think this is a Vimperator issue, rather a Torbutton issue.