This is most annoying! I'll be happily working away when suddenly all my toolbars disappear. At first I had no idea what was going on, and would have to close and reopen FF to get them back, then I discovered that the browser was just switching arbitrarily into full screen mode. I've looked to see if maybe there is something in an inconvenient place that I'm accidentally clicking on to cause this, but no. It just happens for no reason. Is there a fix for this?
Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).
Do NOT click the Reset button on the Safe mode start window or otherwise make changes.