Why does Firefox not have first-class support for Thunderbird?

[thanatica]

When I have Thunderbird installed and I click on a mailto-link, why does Firefox not suggest using that Thunderbird installation as one of the possible ways to handle the link?

Isn't Thunderbird a Mozilla product? Why isn't it listed? Why do I have to look up its executable?

Don't make me think!

Allthewhile, Google and Yahoo are listed, as if I have those 😑

[siffemcon]

That's fixable. Go to TB menu > General > System Integration and click the 'Check Now' button. If it didn't work, post your question at https://support.mozilla.org/en-US/questions/new/thunderbird/form.