Hmm, this isn't a built-in feature of Firefox, but here are a couple possibilities: (1) Maybe Yahoo has a setting for this, but it is stored in a cookie and the cookie got wiped out somehow? (2) Maybe one of your add-ons has a setting for this, but the add-on was disabled during the update because it needs to be updated for Firefox 30? You can check whether any of your extensions are disabled or need updating on the Add-ons page. Either: * Command+Shift+a * "3-bar" menu button (or Tools menu) > Add-ons In the left column, click Extensions. The disabled ones appear toward the bottom on a gray background. To check for extension updates, at the top above the list, click the "gear" button, then Check for Updates. Anything relevant there? ---- The "manual" methods for opening a link in a new tab are: * hold down the Command key while clicking the link * "middle-click" the link with a mouse scroll wheel * right-click the link > Open Link in New Tab If command+click doesn't work, this can indicate that a script attached to the link and is overriding normal Firefox behavior.