I was an early Firefox adopter (about a decade of use, after netscape and Mozilla usage for the previous decade), but switched to Chrome a few years back. With recent improvements I have been trying Firefox again, and overall very happy. But, something I had installed a while back took over my installation. I think it may have been an "anti-adblock" add-on, but can't be sure. The way I know I was hacked is because: 1) When I first upgraded Firefox to 57.0 and restarted the browser, I got a 'your computer has been hacked, you need to click on this link to fix it' scam (with loud siren sound). I had to restart Firefox several times, resetting some extensions, to be able to even use it because this scam was displayed in an uninterruptible window under Firefox (I couldn't enter anything other than information the scam wanted, cancel just restarted the scam prompt). I suspect now that this going away was just the code stopping trying to get information when there was some resistance. 2) Today I tried to login to my coinbase (Bitcoin and related trading) account. After the typical login prompt I expected the normal 2-factor request. But instead, there was a security warning that I needed to 'validate my email account', with a prompt that clearly wanted me to enter my GMail account email and password. This would have given access to one of the ways coinbase validates accounts (but not the SMS verification that I also have enabled). This is definitely not a normal coinbase request, and clearly a hack. With Bitcoin where it is, this hack could be worth 10's of thousands of dollars. I have validated that Coinbase never requests this information through searches, but not directly with Coinbase (nothing online shows them requesting such strange and compromising information). So, I have reverted to using Chrome. I have never had such a hack through Chrome. This is truly nasty and I can't use Firefox with any chance of this happening: I'm effectively trusting you guys with the keys to my kingdom. I've changed passwords, but now I wonder what all this hack may have accessed. Changing all passwords for all accounts Firefox may have seen logins for is an enormous task. So, I have not reset the hacked Firefox, I'm just not running it. It should still have whatever code is there to take over my Coinbase account (and likely more). How do I figure out what happened here? I really would like an alternative to Chrome, but this is not remotely acceptable and has damaged my ability to trust Firefox substantially.