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Message: You can't open the application Firefox because it may be damaged or incomplete

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  • Last reply by cor-el

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I've been using Firefox for a long time. Today I decided to change the settings to delete my history when I closed the window. Now when I try to open up Firefox I get a continuous pinwheel. I deleted Firefox from my computer and reinstalled, but it still won't work. There's now a grey icon titled Firefox with a square and a circle and line through it. When I try to delete this icon, it won't let me, saying Firefox is still running. When I try to open the icon, I get the following message: "You can't open this application Firefox because it may be damaged or incomplete."

Any suggestions on what to do?

I've been using Firefox for a long time. Today I decided to change the settings to delete my history when I closed the window. Now when I try to open up Firefox I get a continuous pinwheel. I deleted Firefox from my computer and reinstalled, but it still won't work. There's now a grey icon titled Firefox with a square and a circle and line through it. When I try to delete this icon, it won't let me, saying Firefox is still running. When I try to open the icon, I get the following message: "You can't open this application Firefox because it may be damaged or incomplete." Any suggestions on what to do?

All Replies (3)

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Do a clean reinstall and delete the Firefox program folder before (re)installing a fresh copy of the current Firefox release.

Download a fresh Firefox copy and save the file to the desktop.

If possible uninstall your current Firefox version to cleanup the Windows registry and settings in security software.

  • Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you lose personal data like bookmarks and passwords from profiles of other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

  • (32 bit Windows) "C:\Program Files\Mozilla Firefox\"
  • (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"

Your bookmarks and other personal data are stored in the Firefox profile folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.

If you keep having problems then also create a new profile.


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I'm likely doing something wrong, but this sounds like what I've already done. Download a new Firefox (for Mac), delete the current version, then run the new version. The problem is the old version doesn't delete (see original post). When I try to open the new version of Firefox, I get an error message and an option to return to factory settings, which I choose. It still does nothing.

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Try to repair the disk permissions:

Download a new copy of the Firefox application and save the disk image file to the desktop

Your personal data is stored elsewhere in the Firefox profile folder, so you won't lose your bookmarks and other personal data when you uninstall and (re)install Firefox.