Hi sog22, this take a little persistence, but here is one method: Open your Outlook mailbox. Then (1) Open Firefox's Web Console in the lower part of the tab below your mailbox. You can do that using either: * Ctrl+Shift+k (Mac: Command+Alt+k) * "3-bar" menu button > Web Developer > Web Console * (menu bar) Tools > Web Developer > Web Console (2) Select and copy the following line of script (it's all one line -- ignore the fact that the forum creates links): navigator.registerProtocolHandler('mailto', 'https://outlook.live.com/mail/deeplink/compose?to=%s', 'Outlook Live'); (3) In the tab with your mailbox, in the Web Console, paste the script and execute it. Here's how: * One-line console (has the caret (>>) at the bottom): paste and press the Enter key * Multi-line console (has the command area on the left side): paste and click the Run button Screenshots of both layouts are attached for reference. ''If this is your first time using the Web Console, Firefox may ask you to take some action to prove you understand it's dangerous to run scripts from strangers. That is true.'' After the script is executed, an infobar should open at the top of the page. Click "Add Application". You now can close the Web Console by clicking the "X" on its top bar at the right. Success?