See https://support.mozilla.org/en-US/questions/1290655 Windows can't find Firefox-follow up

It looks like this is now resolved.

The Refresh Firefox feature can fix many issues by restoring Firefox to its default state while saving your essential information. Consider using it before going through a lengthy troubleshooting process. The Firefox Safe Mode window includes a Refresh Firefox option. You can start Firefox in Safe Mode by holding down the shift key while starting Firefox.

There is some links which also helps after that above https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode#w_safe-mode-window

Thanks

Hi rcitti1, if I understand your solution correctly, you did this:

1. Open the Firefox program folder: C:\Program Files\Mozilla Firefox
2. right-click the file firefox.exe and choose Copy
3. right-click a blank area of the folder and choose Paste -- Windows creates a file named firefox - Copy.exe
4. Double-click firefox - Copy.exe to launch Firefox successfully.

Wow, that's strange.

Over the years, some malware that prevented Firefox from running was fooled by adding a 1 to the file name, i.e., firefox1.exe. While I don't know whether you have malware on your system, it's worth doing some follow-on scans, I think. Our support article recommends some tools for that: Troubleshoot Firefox issues caused by malware.

This is a problem with Avast making changes to some registry keys.

1. Open run (Windows key + r)
2. Type: regedit
3. Navigate/Search to Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Option
4. Delete the (Debugger) folders of the apps that do not work