Member Avatar for Techno22

Firefox is default browser but Thunderbird email links
have stopped opening in the browser in the last few days.
Have tried most of Mozilla's recommendations but nothing
has worked so far.

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There are two distinct failure modes this thread could be describing: links inside Thunderbird messages (http/https) that no longer open Firefox, or clicking mailto: links in the browser that no longer launch Thunderbird. Both share some common isolation steps; they differ when it comes to protocol-registration vs. browser/handler settings. ’s profile/new-account idea is the right deep test, and ’s cleared-history attempt shows simple fixes are worth trying even if they sometimes fail.

Quick isolation checklist (do these before heavy profile surgery):

  1. Copy a URL from a Thunderbird message and paste it into Firefox’s address bar. If that opens, the link itself is fine and the problem is the “click -> OS -> browser” handoff.
  2. From Run or a Command Prompt run these to test the OS protocol handlers:
start "" "https://example.com"
start "" "mailto:test@example.com"

Observe which application opens. If neither opens, Windows protocol association is likely broken.
3. Temporarily make another browser (IE/Edge/Chrome) the default and click a Thunderbird link. If that opens, Thunderbird is handing links to Windows correctly and the problem is Firefox configuration or an extension.
4. Launch Firefox in Safe Mode:

firefox -safe-mode

If links work there, a Firefox extension/handler is interfering.
5. Temporarily disable any antivirus/web‑protection link‑scanning features and retest.

Next-step checks and cautions:

  • For HTTP/HTTPS link failures, check Firefox’s Applications settings (look for http/https actions) and suspect a Firefox add-on if Safe Mode fixes it.
  • For mailto failures, confirm Thunderbird is the registered mail client in Windows and that Firefox’s Applications entry for “mailto” points to Thunderbird (or use the about:config keys beginning with network.protocol-handler to inspect handlers).
  • Avoid editing the registry unless comfortable; export/backup keys first (for mailto, keys under HKEY_CURRENT_USER\Software\Classes or HKEY_CLASSES_ROOT\mailto are relevant).

If these fail, a repair reinstall of Firefox and/or Thunderbird usually restores protocol registrations; if the problem appears only in the old Windows user profile, follow ’s profile/account path and migrate extensions/settings one at a time to locate the culprit.

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Member Avatar for Techno22

Many thanks.
Followed your suggestion but I am afraid that it made no difference.
Firefox is set as the default browser and Thunderbird is set as default
email client.
This problem has been going on for a little over a week now - must be a record for me for fixing an issue - but there is no sign of a solution yet.
Very much appreciate your help.

Member Avatar for LaxLoafer

What happens if you try it from a newly created Windows user account?

Member Avatar for Techno22

Sorry for delay in getting back.
I don't know how to create a new Windows user account.
Also, would I be able to go back to the old one?
How would it affect using other Windows machines?
Thanks for response.

Member Avatar for LaxLoafer

To create a new Windows user account, open a command prompt and type 'control userpasswords2'. The 'User Accounts' dialog box should appear. Select the Users tab and click the 'Add...' button. Alternatively you can find the dialog box through the control panel, or follow Microsoft's guidance: "Creating a user account"

Once you've created the user account you should be able to switch between them by logging off and then on. If fast user switching is enabled (not available on lesser editions of Windows), you can switch between accounts without having to log off first.

Creating a new user account will give you a fresh Windows user profile, and running Firefox will generate a new Firefox profile. If Firefox works as expected that would suggest your installation of Firefox is fine, and also the profile for the Windows user account.

As a next step you could try copying the old Firefox profile across to your new account. Note there will be some file permission issues when attempting to access the other user's account, so you'll need to copy the old profile to a shared location or grant the second account permissions to access the old profile folder.

To find the location of your Firefox profile open up the browser and navigate to 'Help > Troubleshooting Information' > Profile Folder.

You'll need to edit 'profile.ini' to tell Firefox where to find a copy of the old profile. The ini file is normally located in the user's AppData folder, typically something like C:\Users[USER]\AppData\Roaming\Mozilla\Firefox.

Run Firefox with the '-ProfileManager' switch and you should be able to choose which profile to load.

If the old Firefox profile works with the new Windows user account, but still shows the same fault, then it suggests a problem with that profile. You might be able to deduce what the problem is by comparing the bad profile with a working one. Bring the profiles closer together, for example by adding in any plug-ins or extensions you use, one at a time, and hopefully the fault will become apparent.

Good luck and let me know how you get on.

Member Avatar for Techno22

Gosh!
What a huge amount of work you have put in.
Really appreciate your efforts.
As someone who is very much a novice this is going to take
some time.
Thanks for the good wishes, for all the work, and will let you
know how things go.

Member Avatar for Honny flussia 
    You can try to clear your browser history. Open FireFox and then click "Settings" > "History" > "Clear browsing data". quit the browser and sign in it again. At this moment, your email links may become normal.
Member Avatar for Techno22

Afraid that didn't work.
Was worth a try, though.
Thanks.

Member Avatar for LaxLoafer

Have tried most of Mozilla's recommendations but nothing has worked so far.

Techno, it might be worth trying a few more. Millions and millions of people use Firefox so it's quite likely that someone else has encountered the same problem or something very similar.

Have a look at this one on Mozilla's support forum: http://support.mozilla.org/en-US/questions/921787 Please check the entire thread as it contains some info that's related to how mailto links work in Firefox.

I think my earlier troubleshooting advice is a little to involved for a novice, but it's something you might want to return to later on if you do get really stuck. Once you've identified the fault I suspect the fix will actually be quite simple. Keep trying :-)

Member Avatar for Techno22

Many thanks.
I did look extensively at Mozilla's site when the problem first started about a month ago but I will go back and check again in case I missed anything
I will most certainly return to your earlier advice at a later stage.
Yes, indeed, the fix will probably turn out to be quite simple.
No sign of it yet, though!

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