Not long ago my computers both behaved the way I prefer; that is, clicking a link in email caused Firefox (my default browser) to open a new tab and jump in front of Mail. Now, however, the tab opens but I can’t tell because email stays in front. I can’t find anything in preferences for Apple Mail or Firefox that addresses this issue. How do I get back my preferred response to clicking a link?
— Carol Fortlage
Have you changed anything else about your Mac at the time when this happened? Like installing something, like Growl?
Or, it could have simply been a change in behavior on the Firefox side -- something in an update.
If there isn't a setting for it in the Firefox prefs, then there may not be anything you can do. Just quickly option+tab to Mail after you click the link.