Firefox covering taskbar when maximised

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http://superuser.com – Just today, I have noticed that Firefox (updated to 23 for about a week), when maximised, is covering the Windows taskbar, which is quite annoying. After trying a few different applications, I can confirm that only Firefox is doing this. Is there any way to restore normal behaviour? A couple of things I will point out in advance to avoid misunderstandings that seem rife with the troubleshooting pages I have found so far: Firefox is covering the Windows 7 taskbar, not any Firefox toolbars. I am not in fullscreen mode. The "Autohide the taskbar" setting in Windows is off. Things I have tri (HowTos)