Just found: BBC News - Mozilla Firefox browser upgrade taken offline due to vulnerability So I did the Help/About thing to find out which version I had. Thankfully 15.0.1. But no! It started an automatic update! And it tells me that it will take effect after switching off. Presumably that'll be the version that Mozilla are advising users not to download. Not to worry, the BBC story includes a link that purports to show how to revert to 15.0.1. Unfortunately, the page that appears is one that invites you to update to version 16. So, Mozilla don't seem to know what they're doing at the mo and BBC appear not to check the veracity of their links... I suppose I'll just have to find out what happens next time I switch on.