Yep. Hide one of their tweets and then click on 'hide other items like this one' and you'll see the option to hide all tweets from that particular person. - Akiva Moskovitz

As Akiva says. You can hide by one person or hide from all people. - Louis Gray

Wow! thanks, that was fast & effective. Now I can breath freely on FF - Rohit Srivastwa

:((( and how to unmute it???? - Rohit Srivastwa

Rohit: reversing it is not as intuitive as hiding it, but at the bottom of every page, there's a link to show hidden items. If you see one of your friends' tweets there, click "un-hide" on it. It'll undo the global hide from before. - Mark Trapp