Sorry but I do not think you may do as you intend.

Firefox itself does not handle writing emails, although it will do so indirectly if you use web mail with Firefox. Firefox needs to use a mail client. The instructions you found relate to setting the mail client that Firefox uses, if for instance you click an email link on a webpage you are looking at.

• maybe consider downloading, installing and using Mozilla Thunderbird
  • https://www.mozilla.org/en-GB/thunderbird/features
  • https://support.mozillamessaging.com/en-US/kb/switching-thunderbird

Not all of our Knowledge Base articles have specific instructions for Windows 8 yet.

• the general link to the mailto article is
  Change the program used to open email links
  and it should redirect to the most suitable version of the article
• any specific Windows 8 information if/when it exists will be at
  Change the program used to open email links#os=win8&browser=fx19
• note the articles have file selector buttons at the top near to the Firefox icon that allow you to choose document versions for different OS & fx versions.

A Windows 8 article is

• http://windows.microsoft.com/en-us/windows-8/choose-programs-windows-uses-default

Note that explains specifically

You can only use an email program installed on your PC as the default. This means you won't be able to use a web-based email service as the default email program. 

Because Firefox can't handle e-mail you will end up with endless tabs opening if you would set Firefox as the application to handle mail or get an open with dialog, so never do this.

John99 and cor-el,

Thanks so much for your replies. I'm so sorry that I forgot a very important piece of information. I realize that Firefox itself won't handle e-mail. What I neglected to include was the fact that I am a gmail user, and want to use Firefox as a way to handle Mailto links.

Again, sorry for the confusion, and I'm hoping there's a way to do this (there is via Google Chrome, which appears in the list of options for Mailto, but Firefox is absent). Thanks again.

You should be able to set Gmail as the default for the Mailto action in Tools > Options > Applications

• https://support.mozilla.org/kb/change-firefox-behavior-when-open-file

If that isn't possible then delete the mimeTypes.rdf file in the Firefox Profile Folder to reset all file actions.

• http://kb.mozillazine.org/mimeTypes.rdf
• http://kb.mozillazine.org/File_types_and_download_actions#Resetting_download_actions

You can also look at the network.protocol-handler.external.mailto prefs on the about:config page.

• http://kb.mozillazine.org/about:config

If network.protocol-handler.external.mailto prefs are user set (bold) then right-click and Reset them to the default value.

Thanks again for helping me with this. Actually, the Mailto action in Tools > Options > Applications is indeed set to Gmail. However this does not seem to help me if I click on a Mailto link OUTSIDE of Firefox (say, in another browser or in a contact management database I use). When I do that, the awful Windows 8 Metro-based Mail app takes over my screen.

So, in summary, I want to be able to set the Global option in windows 8 (via Control Panel > Default Programs > Associate a file type or protocol with a program > MAILTO) to use Gmail via Firefox. But Firefox doesn't appear in the list. Right now, the only options are Google Chrome, Mail, and "Look for an app in the Store".

Sorry if my question wasn't clear from the beginning, and thanks again for sticking through this with me!

Hi again Tridens,
It is not that your original question was unclear, rather that my answer did not explain properly that you are not going to be able to achive this.*

My first post mentioned webmail (such as gmail) may not be used as the Windows; system wide; default for opening email & mailto links, outside of Firefox.

As it seems you do not like the available alternatives my suggestion was to consider installing and using Thunderbird.
_{(Development on the Thunderbird project has recently ceased, however continuing support is in the process of integration into these Firefox support forums)}

*

Almost anything is possible with computers. Some geek may be able to quickly code a simple intermediary script that may then be associated correctly and proceed to open Firefox at Gmail, that may even be relatively trivial for all I know. However it is beyond my experience, and possibly considered off-topic for this forum.
Recommending Thunderbird seems the best alternative. Click on the prominent "Mozilla" tab above these posts and explore Thunderbird advice.

john99,

OK, I'm clear now. Thanks again for taking so much time to help. I'm very grateful.

Sadly, this is a missing feature. In 2013, a web browser is a mail client. Opera and Chrome both support mailto. Just not Firefox.

I believe you can work around this problem with google's "Gmail Notifier" app. I haven't tried it in Windows 8, and it's not ideal because it uses the taskbar rather than a live tile, but I believe it associates itself with mailto and can then send the link to a browser of your choosing.

Or you could just use Chrome or Opera for external mailto links.

You can check the network.protocol-handler.external.mailto prefs on the about:config page.

• http://kb.mozillazine.org/about:config

If network.protocol-handler.external.mailto prefs are user set (bold) then right-click and Reset them to the default value.