User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:40.0) Gecko/20100101 Firefox/40.0 Build ID: 20150826023504 Steps to reproduce: 1. Firefox running, several tabs open. 2. Open and use another application with a maximized window. 3. Close that other application. OS Name Microsoft Windows 8.1 Pro Version 6.3.9600 Build 9600 System SKU LENOVO_MT_20BX_BU_Think_FM_ThinkPad T450s Processor Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz, 2594 Mhz, 2 Core(s), 4 Logical Processor(s) Installed Physical Memory (RAM) 8.00 GB Name Intel(R) HD Graphics 5500 Driver Version 10.18.14.4206 Actual results: Firefox occasionally reappears showing a mostly blank page (example attached). That page repaints slowly with clicking in the Firefox window. Operation is otherwise normal. Rare event, on the order of weekly. Seems to happen only when other app has (a) maximized window and (b) high system resource usage. Latest case happened on Windows 8.1, but I have also observed it on Windows 10. Expected results: Firefox should have reappeared showing the page that is open.

Is this bug still an issue in FX44.0 or Nightly 47.0a1?

It looks like this bug has now been fixed.

That was premature. No sooner did I post that then I shut down the full screen app, restored Firefox, and while most of the windows was OK, the the Window control icons (top right corner) were missing. (Tried to capture a screenshot, but OneDrive interfered. Color me seriously ****.)

p.s. This is on Windows 7 Pro x64. The full screen app was running in Compatibility Mode, which may be a factor.

(In reply to John Navas from comment #4) > p.s. This is on Windows 7 Pro x64. > The full screen app was running in Compatibility Mode, which may be a factor. Does this happen with any application or is it just specific applications that seem to trigger this? Does running those applications in normal execution mode (ie. not compatibility mode) replicate the issue? Does this happen if you turn off hardware acceleration in Firefox?

Note the missing Window control buttons.

Happened again, uploaded new screenshot: Top of Firefox window showing blank area. 1. Only application currently causing this is Microsoft game Age of Empires The Asian Dynasties. 2. This application will only run in Windows 7 Compatibility Mode AFAIK. 3. Have not tried turning off hardware acceleration. Will try that. p.s. This problem has occurred on different laptops, one with Intel HD Graphics 5500 graphics, this one with NVIDIA NVS 4200M graphics.

If anything, problem is worse with hardware acceleration off.

I've noticed this seems to happen most often when: 1. Firefox running minimized with game full screen in compatibility mode. 2. Quit game, system returns to normal mode. 3. Restore Firefox.