Want to choose the program that opens when you click an email address in Mozilla Firefox or even use web-based email automatically? Find out below how to change the default email program in Firefox.

First, an Invitation from Emperor Elagabalus to Dinner

What an honor! So you go, you see, and you sit.

Half way through the banquet, you find yourself slouching, uncomfortably, under the table—and you took barely a sip of the wine!

Instead of giving you a customary cushion, boy emperor Elagabalus had seated you on a cushion filled with air; air which he, of course, let out of the cushion at an opportune moment.

Now, this information comes to us by way of the entirely untrustworthy Historia Augusta and is itself probably nothing but hot air.

Either way, want to inflate your chances of Firefox launching the right email program—or even the right email service on the web—when you click on an email address? Please, come, sit down and see:

How to Change the Default Email Program in Firefox

To make Mozilla Firefox launch your favorite email program when you click on an email address:

  1. Click the Mozilla Firefox hamburger menu ().
  2. Select Options (or Preferences… on a Mac) from the menu that has appeared.
    • On a Mac: You can also select Firefox | Preferences… from the menu or press Command ,.
    • Tip: As an alternative, type about:preferences in the Mozilla Firefox address bar and press Enter.
  3. Under Applications, find and highlight mailto in the Content Type column.
    • Tip: You can start typing mailto over Search files or applications on top of the list of applications.
  4. Click the currently selected application in the Action column.
  5. Choose the desired email program or service from the menu that has appeared.
    • Note: On Windows and macOS, Mozilla Firefox uses the default email program as its default as well. Its choice will appear with (default) appended to its name.
      If you change the default Windows email program, the (default) email program in Mozilla Firefox will also change. Instead of adding an email program to Mozilla Firefox, it is usually best to use the Windows default and change that using Windows settings.
      Similarly, if you change the default macOS email program, the (default) email program automatically changes in Mozilla Firefox, and altering the macOS default it preferable to adding a new email program to Mozilla Firefox.
    • Tip: You can add additional web-based email services; see below.
  6. Close the Options (or Preferences) tab or window.

How to Change the Default Email Program in Firefox: FAQ

Can I add additional email services—such as FastMail or iCloud Mail—to Mozilla Firefox?

Yes, this is often possible.

To add a web-based email service so you can make it the default email program in Mozilla Firefox:

  1. Open the email service’s page in Mozilla Firefox.
  2. Click the Mozilla Firefox hamburger menu icon ().
  3. Select Web Developer | Web Console from the menu that has appeared.
    • Keyboard shortcut: You can also press Control Shift K (Windows and Linux) or Command Shift K (Mac).
  4. In the Console window’s command line (following the >> prompt), type a command made up of the following parts:
    • navigator.registerProtocolHandler(
    • “mailto”,
      • Note: Do not change the two preceding elements.
    • “[URI]”,
      • Important: Replace [URI] this with the link to compose a new message in the email service. In the link, %s will be replaced with the email address on which you click in Mozilla Firefox to start an email.
      • Note: Do make sure the domain for the URI corresponds to the domain currently open in Mozilla Firefox; e.g., if you are on https://mail.google.com, the URI needs to start with https://mail.google.com.
      • Example: The URI for Gmail to start a new message is “https://mail.google.com/mail/u/0/?hl=en&view=cm&tf=1&fs=1&to=” followed by the email address, so the whole URI would be “https://mail.google.com/mail/u/0/?hl=en&view=cm&tf=1&fs=1&to=%s”.
      • Alas: There is, unfortunately, no standard way these addresses are set up; here’s a list of direct links to many composing new emails in many popular web-based email services, though.
    • “[Name]”)
      • Tip: Replace [Name] with the name of the email service.
      • Example: Use “Gmail” for Gmail.
    • Full Example: The full command for setting up Gmail as an email service in Mozilla Firefox is: navigator.registerProtocolHandler("mailto", "https://mail.google.com/mail/u/0/?hl=en&view=cm&tf=1&fs=1&to=%s", "Gmail")Adding a web-based email service as mailto handler in Mozilla Firefox
  5. Hit Enter.
  6. Under Add [Name] as an application for mailto links? (which appears above the currently open page in Mozilla Firefox), select Add Application.

Now, you can make the newly added web-based email service the default email application in Mozilla Firefox using the steps above.

(How to change the default email program in Mozilla Firefox tested with Mozilla Firefox 62; updated October 2018)