This happens regularly for me, about 3 or 4 times per day. It used to be exclusively when I'm visiting https://translate.google.com. Today, however, it is also happening on twitter.com. When it happens however, it has always been when I'm navigating to one of those domains in open tab that I was using. Also, it has always been when I'm relying on the bar's autocomplete (for example, when I start typing "tra" and the rest is auto completed to translate.google.com) and I tap the Enter key. No amount of refreshes fixes the problem even if I disable cache (I disabled it from the network inspector in the web developer tools). There's only one warning message in the console saying "This error page has no error code in its security info". Also, even if I change URLs while under any of these 2 domains in that "broken" tab, I keep getting a blocked page. Changing to another domain, for example, google.com works. For example, If I change from https://translate.google.com to: - https://twitter.com gives a broken page - https://twitter.com/firefox gives a broken page - https://translate.google.com/?sl=auto&tl=en&text=Hello%20word&op=translate gives a broken page - https://support.mozilla.org works However, if I just go to the url bar and tap "Alt" + "Enter", the page successfully opens in a new tab. I'm using Firefox on Mac.