Hi, for reference here is an article about [[Private Browsing - Use Firefox without saving history]]. If you aren't seeing the 'mask,' try Firefox Safe Mode to see if the problem goes away. [[Troubleshoot Firefox issues using Safe Mode|Firefox Safe Mode]] is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). '''If Firefox is open,''' you can restart in Firefox Safe Mode from the Help menu: * Click the menu button [[Image:New Fx Menu]], click Help [[Image:Help-29]] and select ''Restart with Add-ons Disabled''. '''If Firefox is not running,''' you can start Firefox in Safe Mode as follows: * On Windows: Hold the '''Shift''' key when you open the Firefox desktop or Start menu shortcut. * On Mac: Hold the '''option''' key while starting Firefox. * On Linux: Quit Firefox, go to your Terminal and run ''firefox -safe-mode'' <br>(you may need to specify the Firefox installation path e.g. /usr/lib/firefox) When the Firefox Safe Mode window appears, select "Start in Safe Mode". ;[[Image:SafeMode-Fx35]] '''''If the issue is not present in Firefox Safe Mode''''', your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems]] article to find the cause. ''To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.'' When you figure out what's causing your issues, please let us know. It might help others with the same problem. Thank you!

Thanks for your help. Starting in safe mode did not fix the problem but, as it proposed also to refresh Firefox, I tried that solution after two restartings in Safe mode. And that fixed the problem. Best of all, the system automatically installed my plugins and I continue to have the purple mask. Great ! Thank you ! Ladislas