When I start Firefox to a maximized browser window, press the Unmaximize Window button on the window frame to unmaximize the window, and then go to another window and come back to the browser window, the browser window resizes to fill up the screen, becoming "pseudo-maximized", although it remains unmaximized as far as the window manager is concerned. The bug doesn't happen if I start the browser to an unmaximized window, nor does it occur more than once in a browser session. But it occurs consistently the first time I unmaximize the window if it started out maximized. It doesn't matter which window I switch to. It can be another Firefox window (Preferences dialog, the Error Console, etc.) or some other application window. An even simpler way to reproduce the problem is to use a keyboard shortcut to unmaximize the window. Just press Alt-F5 (or Alt-Space x). The window will go from maximized to unmaximized to pseudo-maximized all in one go. Steps to Reproduce: 1. start Firefox with one browser window open; 2. unmaximize the browser window; 3. resize the browser window to fill an obviously smaller portion of the screen than a maximized window; 4. maximize the window; 5. restart the browser; 6. unmaximize the window by pressing Alt-F5, Alt-Space x, or clicking the unmaximize button; 7. if you clicked the button, switch to another window and back again. Expected Behavior: windows stays unmaximized. Actual Behavior: window becomes pseudo-maximized.
This sounds like what I see a lot after I restore my session.