Set up Gmail as Your Default Email in Firefox for macOS
Change the settings in Firefox to make Gmail the default for mailto: links.
In the upper-right corner of browser, select menu (three lines). Select Preferences. You can also enter about:preferences in the Firefox address bar instead of clicking this menu item. Go to the General tab. In the Applications section, select the Mailto drop-down menu, and choose Use Gmail. Close the Preferences tab to return to your browsing session. Gmail is now your default email client in Firefox.
Set up Gmail as Your Default Email in Firefox for Windows
Setting Gmail to your default in Windows differs slightly.
Select the menu (three lines). Select Options. You can also enter about:preferences in the Firefox address bar instead of clicking this menu item. In the General Preferences, scroll down to the Applications section, and select the mailto option in the Content Type column to highlight its corresponding row. Select the drop-down menu in the Action column. Choose Use Gmail from the list of options. Close the Preferences tab to return to your browsing session. Gmail is now your default email client in Firefox.
