First let's make sure Firefox has closed completely. Open Task Manager by pressing Ctrl+Shift+Esc in Windows, go to the ''Processes'' tab and look for "firefox.exe" to see if an instance is still running. If no Firefox instance is running and the bar is still visible, this is something that is outside Firefox (as you already indicated it appears on your desktop and overlaps other programs, namely Chrome). If this is independent from Firefox, I would recommend a malware sweep as your first step: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware#w_how-do-i-get-rid-of-malware_2. Run all the scanners, as one may catch what the other did not. If the problem persists after the malware cleanup, it may be a legitimate program you will need to uninstall from Windows. I do not recognise the style, so I cannot give instructions for doing so.