Setting Program defaults does not work in my Windows 10

jagman said:

...My Firefox accepted your changes, so did the registry.

But the DEFAULTS, by Protocol, etc ONLY offer the Store or MAIL

Have you restarted the PC yet? You probably need to before the Firefox mailto key takes effect.

Also on the Protocol screen, mine shows:
MAILTO
URL:mailto

While yours is:
MAILTO
URL:mailto PROTOCOL

MY OS VERSION IS: 15063.850
Is yours newer? older?

Mine (and, by the looks of it @pepanee's) are how they look in Fall Creators update (1709, os build 16299...). Yours is Creators Update (1703). But I have Anniversary Update (1607, 14393...) on my test machine at the moment and that too says:
MAILTO
URL:MailTo Protocol

....odd, but probably not significant. Try the restart and if you can then select Firefox I expect it to work just the same...

Callender said:

In Firefox the email client used to open links is set in Firefox preferences - not Windows Default Programs.

Yes, but if you want to use Firefox as the email client from a mailto link anywhere else in Windows, not just from a webpage in Firefox, then it also needs to be set as the default mailto handler.

As I said in post #5, after setting it as the default handler...

Firefox itself need to be configured to handle a mailto:

Edwin said:

I can set it manually in W7 but in Windows 10, it won't assign a protocol ID.

That's because Firefox's Setup doesn't register Firefox as capable of handling the MAILTO Protocol. To make Firefox available in the list for setting a default app by protocol you need to add a registry entry for Firefox to say that it does. I first described how to do that in post #29 here:

Mailto: in Browsers not working

Edwin said:

...Can't sign out of your web-mail though, cuz then it becomes a pita.
I wonder if Firefox does that as a preventative security measure?

Staying signed in to your webmail is a matter of ticking a 'remember me' or 'stay signed in' box. Firefox only comes into the equation if you've set it to delete all cookies on exit - that includes the webmail's login cookie.

I normally leave my Yahoo signed in on closing Firefox, but if I do log out, then clicking a mailto link just adds the login page to get past before I get to the 'compose email' page with the address all ready filled in.

Edwin said:

Much easier to just install a client!

Webmail is sufficient for my needs - I can't be bothered to install a client (or use MS's Mail) just to get mailto links to work :)

As a postscript to this thread - I've just searched for and found this thread. The reason being I've just done a clean install of 1803 and Firefox 60.0.2 on a new machine and wanted to refer to my notes in post #5 to find the correct registry key to modify.

Bree said:

Unless thing have changed with the latest version, Firefox's Setup doesn't register Firefox as being capable of handling the MAILTO protocol (even though it can). Without this setting in the Registry Firefox doesn't appear in the list of available apps when you try to set up MAILTO. You can edit the registry to add the mailto protocol to Firefox's capabilities.

This is how I fixed it so that I can use Firefox whenever I click a mailto: link using 'choose default applications by protocol'. You'll find this if you scroll down to the bottom of 'defaults apps'.

In the case of Firefox, a new String named mailto should be added to the key HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\FIREFOX.EXE\Capabilities\URLAssociations with the value FirefoxURL (the same value as all the existing strings there). In addition, Firefox itself need to be configured to handle a mailto: by opening your chosen webmail service (or whatever else you use). For Firefox the relevant setting are found by putting...

about:Preferences#applications

...in the address bar

Mailto: in Browsers not working

A couple of notes to add:

• The registry key may have a different name. On this new machine it was still called 'Firefox...' but had a string of characters after that instead of '.exe'. This also applies to the value for the mailto string, just make it the same as all the others there. Mine was: HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\Firefox-308046B0AF4A39CD\Capabilities\URLAssociations with the value required for mailto being FirefoxURL-308046B0AF4A39CD
• I can confirm that a clean install of Firefox still doesn't announce its mailto capability in this key.
• I can also confirm that a restart is required before the changes take effect