Firefox has a built-in feature, but Yahoo might not accept the subject line and URL in the format Firefox sends it. ''Built-in Feature'' There is an "Email Link" button available in the Customize panel. You can drag it to the main toolbar. See: [[Customize Firefox controls, buttons and toolbars]]. Alternately, "Email Link" is available on the classic File menu. If you do not normally display the classic menu bar (File, Edit, View...), you can tap the Alt key or F10 key to display it temporarily. ''Add-on Workaround'' If Yahoo still isn't accepting the data in the format Firefox sends it, you could try my add-on, which integrates through the right-click context menu. https://addons.mozilla.org/firefox/addon/yahoo-mail-email-link-fix/ If you give it a test, let me know if you run into any problems.