Info on setting up Gmail as the default using Firefox?

I am looking to configure W10 Pro 1809 to use Gmail as the default mailbox, opened in Firefox which is already the default browser.
The are numerous web articles but their instructions refer to menu objects that were renamed and moved. So, I got nowhere.
Can anyone please point me towards some up to-date info, and I shall be on my way.

about://config then search in the search box for mailto. Or just follow this. Change the program used to open email links | Firefox Help

Thanks for the reply, but in about:config there are 6 settings that deal with mailto https:// links, out of 11 that mentions mailto. Four of the settings are set to: ''chrome://browser-region/locale/region.properties''
As for the linked Firefox support article, it is not detailed enough. Wish the volunteer who wrote it, would have tried his own instructions and provided more detail.

I've been at the list of mail defaults and noticed that I have an Outlook account with my gmail address and it is not removable. Then, there is a "Google" (not gMail) option, which asks for my gmail password and the Google mail server settings. To me, this means that they want to me use Outlook as the front end.

I am not comfortable to give MS my password and also dislike Outlook. (aka MS Goulash).

P.S: Gmail has always been my Firefox email preference.

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Did this as well and rebooted. Windows Default programs for Mail lists: Windows 10, Vivaldi, and Look for an app in the MS store. Firefox or Gmail do not exist
https://answers.microsoft.com/en-us/...1-84d18a02dc18

"Win + R", lauch "regedit" and go to "HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\FIREFOX.EXE\Capabilities\URLAssociations" . Then add a string value named "mailto" with "FirefoxURL" as value.

This is the solution. Please see the attached images.