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Firefox won't start, can't work out why

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Having some trouble with Firefox and I'm at my wits end on how to fix it. Clicking the Firefox icon in Windows 10 (whether that's in the Start menu, the taskbar or the app itself in Program Files) won't launch Firefox. The blue loading spinner appears briefly next to the pointer, then disappears. Sometimes a Firefox process appears in Task Manager then instantly disappears, but sometimes it doesn't. Here's what I've tried so far:

- Restarting - Reinstalling - Deleting my Firefox profile and all Firefox app files - Launching in safe mode by holding shift - Launching in safe mode by adding the "-safe-mode" comment - Running as administrator - Checking it's not being blocked by antivirus - Loading the Firefox profile manager by typing "firefox.exe -P" in the run dialog box. This does the same as trying to load Firefox - nothing happens

I can't think what else to do. It may be a coincidence, but my primary monitor died, I restarted the PC and then Firefox wouldn't work. I can't see how it could be related, but who knows.

Anyway, any help would be greatly appreciated!

Having some trouble with Firefox and I'm at my wits end on how to fix it. Clicking the Firefox icon in Windows 10 (whether that's in the Start menu, the taskbar or the app itself in Program Files) won't launch Firefox. The blue loading spinner appears briefly next to the pointer, then disappears. Sometimes a Firefox process appears in Task Manager then instantly disappears, but sometimes it doesn't. Here's what I've tried so far: - Restarting - Reinstalling - Deleting my Firefox profile and all Firefox app files - Launching in safe mode by holding shift - Launching in safe mode by adding the "-safe-mode" comment - Running as administrator - Checking it's not being blocked by antivirus - Loading the Firefox profile manager by typing "firefox.exe -P" in the run dialog box. This does the same as trying to load Firefox - nothing happens I can't think what else to do. It may be a coincidence, but my primary monitor died, I restarted the PC and then Firefox wouldn't work. I can't see how it could be related, but who knows. Anyway, any help would be greatly appreciated!

Chosen solution

hi, the symptoms sound very similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1590430 - did you ever use comdo security products in the past or even if not, could you check if there's a file called IseGuard64.dll, IseGuard32.dll or similar located under C:\Windows\system32\ or your system drive?

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Additional System Details

Installed Plug-ins

LastPass uBlock Origin

Application

  • User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.140 Safari/537.36 Edge/17.17134

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FredMcD
  • Top 10 Contributor
4267 solutions 59835 answers

Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

  • Make sure your Internet security software is up-to-date (i.e. you are running the latest version).
  • Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}

Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again; * Make sure your Internet security software is up-to-date (i.e. you are running the latest version). * Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see '''[https://support.mozilla.org/en-US/kb/configure-firewalls-so-firefox-can-access-internet Configure firewalls so that Firefox can access the Internet.]''' {web link}
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Question owner

Hi FredMcD, thanks for your suggestions. I tried removing Firefox from McAfee's firewall list (for some reason it was in the list twice), but still no luck. I also followed the instructions in the link you supplied re. setting Firefox's incoming and outgoing permissions to "open to all devices", but that didn't work either :(

Hi FredMcD, thanks for your suggestions. I tried removing Firefox from McAfee's firewall list (for some reason it was in the list twice), but still no luck. I also followed the instructions in the link you supplied re. setting Firefox's incoming and outgoing permissions to "open to all devices", but that didn't work either :(
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Question owner

In case anyone comes across this later, it was Firefox 71 that seems to be the culprit. I rolled back to Firefox 70.0.1 and that works perfectly. No idea why Firefox 71 was so broken for me.

In case anyone comes across this later, it was Firefox 71 that seems to be the culprit. I rolled back to Firefox 70.0.1 and that works perfectly. No idea why Firefox 71 was so broken for me.
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alexblake2 said

In case anyone comes across this later, it was Firefox 71 that seems to be the culprit. I rolled back to Firefox 70.0.1 and that works perfectly. No idea why Firefox 71 was so broken for me.

I have the same exact problem. 70.0.1 Ok 71 doesn't start

I tried a fresh install after completely uninstalled the previous version and doesn't start.

Can i ask you what is your CPU?

''alexblake2 [[#answer-1270706|said]]'' <blockquote> In case anyone comes across this later, it was Firefox 71 that seems to be the culprit. I rolled back to Firefox 70.0.1 and that works perfectly. No idea why Firefox 71 was so broken for me. </blockquote> I have the same exact problem. 70.0.1 Ok 71 doesn't start I tried a fresh install after completely uninstalled the previous version and doesn't start. Can i ask you what is your CPU?
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Question owner

Hi

My CPU is an i7 6700K.

Did you try using something like Revo Uninstaller? I was recommended to try that so that it clears out any lingering registry entries. In the end I didn't need to, as 70.0.1 works fine for me.

If I were you I'd stick with 70 for now and see if there's an update to 71 to fix this issue.

Hi My CPU is an i7 6700K. Did you try using something like Revo Uninstaller? I was recommended to try that so that it clears out any lingering registry entries. In the end I didn't need to, as 70.0.1 works fine for me. If I were you I'd stick with 70 for now and see if there's an update to 71 to fix this issue.
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philipp
  • Top 25 Contributor
  • Moderator
5320 solutions 23501 answers

Chosen Solution

hi, the symptoms sound very similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1590430 - did you ever use comdo security products in the past or even if not, could you check if there's a file called IseGuard64.dll, IseGuard32.dll or similar located under C:\Windows\system32\ or your system drive?

hi, the symptoms sound very similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1590430 - did you ever use comdo security products in the past or even if not, could you check if there's a file called IseGuard64.dll, IseGuard32.dll or similar located under C:\Windows\system32\ or your system drive?
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q5idpgvqzf 0 solutions 2 answers

philipp said

hi, the symptoms sound very similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1590430 - did you ever use comdo security products in the past or even if not, could you check if there's a file called IseGuard64.dll, IseGuard32.dll or similar located under C:\Windows\system32\ or your system drive?


Ok problem resolved Thank you

''philipp [[#answer-1270830|said]]'' <blockquote> hi, the symptoms sound very similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1590430 - did you ever use comdo security products in the past or even if not, could you check if there's a file called IseGuard64.dll, IseGuard32.dll or similar located under C:\Windows\system32\ or your system drive? </blockquote> Ok problem resolved Thank you
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Question owner

philipp said

hi, the symptoms sound very similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1590430 - did you ever use comdo security products in the past or even if not, could you check if there's a file called IseGuard64.dll, IseGuard32.dll or similar located under C:\Windows\system32\ or your system drive?

Turns out there's iseguard64.dll in my System32 folder. Last modified two years ago, don't know where it came from through as I've not used Comodo products for many years. Can this file be safely deleted?

''philipp [[#answer-1270830|said]]'' <blockquote> hi, the symptoms sound very similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1590430 - did you ever use comdo security products in the past or even if not, could you check if there's a file called IseGuard64.dll, IseGuard32.dll or similar located under C:\Windows\system32\ or your system drive? </blockquote> Turns out there's iseguard64.dll in my System32 folder. Last modified two years ago, don't know where it came from through as I've not used Comodo products for many years. Can this file be safely deleted?

Modified by alexblake2

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philipp
  • Top 25 Contributor
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5320 solutions 23501 answers

yes, please remove it - afterwards firefox will hopefully be back in working order.

yes, please remove it - afterwards firefox will hopefully be back in working order.
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Question owner

Thanks, that seems to have fixed it! I really appreciate the help.

Thanks, that seems to have fixed it! I really appreciate the help.
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philipp
  • Top 25 Contributor
  • Moderator
5320 solutions 23501 answers

you're very welcome, i'm glad that you have back your firefox :))

you're very welcome, i'm glad that you have back your firefox :))
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