How to Close All Firefox Windows at Once Jan 6, 2021, 9:00 am EDT | 1 min read If you’re like us, it’s easy to end up with 20 Mozilla Firefox windows full of hundreds of tabs open at once. Luckily, there’s an easy way to close multiple Firefox windows at the same time. Here’s how to do it on Windows, Linux, and Mac. So, you’re researching an obscure medical condition or your doctoral thesis, and you’ve opened dozens of Firefox windows. You’ve made a mess of your desktop and you’d like to close them all quickly without having to tediously “X” out each one.