How to set Firefox as the default browser under Windows 10 when it does not show up in the default program list under “Default apps”

 

1 Summary: after re-install Firefox (version 65.01 64-bit), I cannot set it as the default browser of Windows 10. It turned out that the registry entry of Firefox was messed up.

1.1 symptoms

  • under Windows 10, Firefox did not appear in the program list under “Default apps”Set_FF_default_browser
  • after the fix, Firefox reappeared in the program list

1.2 the two major Firefox registry entries are: FirefoxHTML, FirefoxURL

1.3 detailed settings

  • FirefoxHTML
    Windows Registry Editor Version 5.00
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML]
    @="Firefox Document"
    "FriendlyTypeName"="Firefox Document"
    "EditFlags"=dword:00000002
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\DefaultIcon]
    @="C:\\Program Files\\Mozilla Firefox\\firefox.exe,1"
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\shell]
    @="open"
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\shell\open]
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\shell\open\command]
    @="\"C:\\Program Files\\Mozilla Firefox\\firefox.exe\" -osint -url \"%1\""
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\shell\open\ddeexec]
    @=""
    
    
  • FirefoxURL
    Windows Registry Editor Version 5.00
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL]
    @="Firefox URL"
    "FriendlyTypeName"="Firefox URL"
    "URL Protocol"=""
    "EditFlags"=dword:00000002
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL\DefaultIcon]
    @="C:\\Program Files\\Mozilla Firefox\\firefox.exe,1"
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL\shell]
    @="open"
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL\shell\open]
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL\shell\open\command]
    @="\"C:\\Program Files\\Mozilla Firefox\\firefox.exe\" -osint -url \"%1\""
    
    [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL\shell\open\ddeexec]
    @=""
    

1.4 how I figured out this is the issue

  • I compared the settings of Chrome, which also has ChromeHTML and ChromeURL
  • I also found the FirefoxHTML and FirefoxURL entries, but the original settings were strange (the “kernel32::GetLongPathNameW” lines below):
    • FirefoxHTML
      Windows Registry Editor Version 5.00
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML]
      @="Firefox HTML Document"
      "FriendlyTypeName"="Firefox HTML Document"
      "EditFlags"=dword:00000002
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\Application]
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\DefaultIcon]
      @="C:\\Program Files\\Mozilla Firefox\\firefox.exe,0"
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\shell]
      @="open"
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\shell\open]
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\shell\open\command]
      @="\"kernel32::GetLongPathNameW(w R8, w .R7, i 1024)i .R6\" -osint -url \"%1\""
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML\shell\open\ddeexec]
      @=""
      
    • FirefoxURL
      Windows Registry Editor Version 5.00
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL]
      @="Firefox URL"
      "FriendlyTypeName"="Firefox URL"
      "URL Protocol"=""
      "EditFlags"=dword:00000002
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL\DefaultIcon]
      @="kernel32::GetLongPathNameW(w R8, w .R7, i 1024)i .R6,1"
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL\shell]
      @="open"
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL\shell\open]
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL\shell\open\command]
      @="\"kernel32::GetLongPathNameW(w R8, w .R7, i 1024)i .R6\" -osint -url \"%1\""
      
      [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL\shell\open\ddeexec]
      @=""
      
  • I also found in the registry another pair of FirefoxHTML-XXXXX and FirefoxURL-XXXXX (with XXXXX being a random alphanumeric string). So I thought, maybe the messy FirefoxHTML and FirefoxURL were from the old installation, and the -XXXXX version were the correct version.
    • I then just backed up the messy registry entries, removed them, and renamed the -XXXXX version into FirefoxHTML and FirefoxURL
    • PROJ-DONE then problem solved
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