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"Couldn't find mozilla runtime"

New Contributor

"Couldn't find mozilla runtime"

I get error "couldn't find mozilla runtime" at start up,when pc is ready to use,this message comes up! I have read topics about it and also tried several things! Firefox is my default browser! Also I have tried uninstall and then install it again,but when i uninstalled mozilla and then reboot system,message came up again,even mozilla was uninstalled,then i downloaded latest version and installed it again but message still comes up at start up,I don't know what to do with it...

Regular Contributor

Re: "Couldn't find mozilla runtime"

I found this wacky error happens sometimes on corrupted Firefox setups.

Try first to fully uninstall Firefox and delete all profiles (see Uninstall Firefox from your computer).

Another possible reason for the problem is that a shortcut is setting Firefox working path to some path different than Firefox setup path - try to go to Program Files\Mozilla Firefox\firefox.exe or similar in setup path to test if running directly the binary works.

Finally, consider installing Firefox on another partition or hard drive, or using Firefox Portable (

Did any of the above steps solve your problem? Please tell us!

Site Moderator

Re: "Couldn't find mozilla runtime"

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.

Uninstall your current Firefox version, if possible, 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.

Legendary Contributor

Re: "Couldn't find mozilla runtime"

This Microsoft utility reveals the programs that run at startup. Do you notice anything unexpected??

Autoruns for Windows

New Contributor

Re: "Couldn't find mozilla runtime"

First press 'start' , programs', then 'click' on the program 'firefox', press [uninstall]. After that press 'start' again and click 'Configuration' select Mozilla Firefox if it's still there, choose the option 'delete'. -Then restart your computer. When your computer starts -up you'll see the same error but don't worry. -Now you click start and press on 'Computer, in the right collumn. -Then 'Windows (CSmiley Happy' You will see Program Files, Program Files (x86) and probably also Program Files (x86) (x86) -Click on each separately one by one and find the map 'Mozilla Firefox', if it is just [delete] the map or maps. Restart your computer after you checked in all maps called 'Program Files'. Now there will be no error "Couldn't find Mozilla Runtime" anymore and you can install Mozilla Firefox again so it will work fine as it should be . Let me know if it solved your problem.

New Contributor

Re: "Couldn't find mozilla runtime"

Are you talking about runtime error r6034 or other runtime error code. Most commony this error occurs when manifest files become unresponsive or not working. It is due to missing registry entry or damaged, broken or deleted system files. Helpful resource:

Moderator removed link to website offering paid software. The software  on this site is unnecessary and the issue can be repaired without the need for a paid "license." The website further copies the Microsoft logo in an attempt to deceive users. See the forum rules (second to last bullet)
Legendary Contributor

Re: "Couldn't find mozilla runtime"

Hi markjamessmith, I think is not a trustworthy site. It uses a copy of Microsoft's banner image (logo and name), which seems calculated to deceive visitors into believing that it is a Microsoft site.