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Firefox will not run on Mac Catalina 10.15.6

  • 4 replies
  • 1 has this problem
  • 2 views
  • Last reply by Dan_Moss

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I have used Firefox since before it was called Firefox. For the last 3 years I have been using it without problem on my 2017 iMac 27". Suddenly a few days ago I started getting this a message 'The application “Firefox.app” can’t be opened.' I have uninstalled, including removing all folders and files containing Firefox or Mozilla and reinstalled versions 75.0b9, 79.0 and 80.ob5. None of which worked. None will open in safe mode. However, if I boot my computer in safe mode, it works. Return to standard mode and nothing. I have followed every suggestion I can find on Firefox's site and Apple's site. It just plain doesn't work. I love Firefox, hate Safari and tolerate Chrome. I would appreciate some help.

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Hi Dan, I'm not familiar with Safe Mode on a Mac, but if it's similar to Windows, some programs and services that usually start automatically with MacOS may have been skipped. So that would be one area for potential investigation if you can figure out what programs/services those would have been.

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I was using Firefox up until a week or so ago. It then flashed a message on the screen about harmful files and subsequently it has not been able to start. I'm thinking that I have not deleted some residual file. Do you have an app that would thoroughly remove every file associated with Firefox or can you tell me where to find what so I can remove them.

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I think there is a system-level MacOS feature that can block programs from running and Firefox might have gotten added to that list when you saw that warning. If you call up the dialog pictured in this article on your Mac, does it have an indication anywhere that Firefox is blocked:

https://support.apple.com/en-us/HT202491

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No, there is no mention of any products there. I had checked that some days ago. Still I appreciate that you are looking at the possibilities.

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