I just updated to Firefox 33.0 and now the titlebar is transparent (I can see a blurry desktop through it) and there are no more close/maximize/minimize buttons.
Tried restarting Firefox with add-ons disabled and the problem persists.
Using WindowBlinds 8.06 on Windows 7 64-Bit Professional.
Edit: kruglovmaxim has posted a clever temporary fix below.