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Why can't I open firefox on starting windows 10?

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Firefox has been working for months perfectly, since yesterday where I meddled with user rights. I reversed everything back to normal, meaning my User has admin rights and I can access and write over everything. However whenever I start my laptop anew and I open Firefox fresh it says "Another instance of Firefox is already running". When I click on "End task" it keeps spamming the same message. When I go to abort it just ends the firefox.exe (as observed through task manager). When I press windows+r buttons and type in firefox.exe -p or similar, I can create a new account (the last one created did not save, default user cannot be picked) and use Firefox normally. I am super confused and cannot find any solution online, I have tried many and this is the compromise I am working with as of now.

Firefox has been working for months perfectly, since yesterday where I meddled with user rights. I reversed everything back to normal, meaning my User has admin rights and I can access and write over everything. However whenever I start my laptop anew and I open Firefox fresh it says "Another instance of Firefox is already running". When I click on "End task" it keeps spamming the same message. When I go to abort it just ends the firefox.exe (as observed through task manager). When I press windows+r buttons and type in firefox.exe -p or similar, I can create a new account (the last one created did not save, default user cannot be picked) and use Firefox normally. I am super confused and cannot find any solution online, I have tried many and this is the compromise I am working with as of now.
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Additional System Details

Installed Plug-ins

  • Shockwave Flash 28.0 r0

Application

  • User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:66.0) Gecko/20100101 Firefox/66.0

More Information

FredMcD
  • Top 10 Contributor
4126 solutions 57598 answers

Separate Security Issue: Update your Flash Player or remove it using these links; Uninstall Flash Player | Windows {web link} Uninstall Flash Player | Mac {web link}

Note: Windows users should download the ActiveX for Internet Explorer. and the plugin for Plugin-based browsers (like Firefox).

Note: Windows 8 and Windows 10 have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the ActiveX.

Flash Player Version 32.0.0171

https://get.adobe.com/flashplayer/ Direct link scans current system and browser Note: Other software is offered in the download. <Windows Only>

https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download. <Windows Only> +++++++++++++++++++ See if there are updates for your graphics drivers https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration

'''Separate Security Issue:''' Update your Flash Player or remove it using these links; [http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html Uninstall Flash Player | Windows] {web link} [http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html Uninstall Flash Player | Mac] {web link} '''Note: Windows users''' should download the '''ActiveX''' for ''Internet Explorer.'' '''and''' the '''plugin''' for ''Plugin-based browsers'' (like Firefox). '''Note: Windows 8 and Windows 10''' have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the ActiveX. Flash Player '''Version 32.0.0171 ''' https://get.adobe.com/flashplayer/ Direct link scans current system and browser '''Note: Other software''' is offered in the download. <Windows Only> https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) '''Note: Other software''' is offered in the download. <Windows Only> +++++++++++++++++++ See if there are updates for your graphics drivers https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration
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FredMcD
  • Top 10 Contributor
4126 solutions 57598 answers
https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save '''Note:''' Some software, '''like''' Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software. https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding https://www.basezap.com/cant-open-firefox-because-a-copy-of-firefox-is-already-open-mac/ https://apple.stackexchange.com/questions/196771/cant-open-firefox-because-a-copy-of-firefox-is-already-open http://kb.mozillazine.org/Firefox.exe_always_open
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Question owner

Hallo,

thank you FredMcD for the solutions you offered! It took a while to find a work around: creating a new profile and linkin the new profile to the directory in the profiles.ini file. Now it all works well again. I could even just copy the content of the old profile into the new one, so nothing lost. There is still the mystery of why the profile manager wouldn't show the previously created profiles, even though the user folders exist in the Firefox folder in the Appdata directory and what caused the faulty defaultuser in the first place.

On the screenshot the error says "Firefox cannot use the profile "default" as the user is already being used." which is strange because there is no Firefox instance running in the first place.

Hallo, thank you FredMcD for the solutions you offered! It took a while to find a work around: creating a new profile and linkin the new profile to the directory in the profiles.ini file. Now it all works well again. I could even just copy the content of the old profile into the new one, so nothing lost. There is still the mystery of why the profile manager wouldn't show the previously created profiles, even though the user folders exist in the Firefox folder in the Appdata directory and what caused the faulty defaultuser in the first place. On the screenshot the error says "Firefox cannot use the profile "default" as the user is already being used." which is strange because there is no Firefox instance running in the first place.
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