When I start **answering** a question on superuser, with Firefox 11 on OSX 10.7, **then swipe back** (two finger swipe using the touchpad on my macbook), I get the following notice. It seems like a javascript-alert. The catch: neither of the buttons work. The only way to get out of there is to kill the browser. I've had this twice today. It seems like a javascript-bug. I cannot close the window, or switch to other tabs, although other windows keep on working. 

When I start a new question, this works like it should. I can go back to the previous page, no warning. 

When I use the back-button in the browser, it works like expected.

![Screenshot of the popup][1]


  [1]: https://i.sstatic.net/8p9A8.png


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**Safari (OSX)**

I just tested the same situation with Safari. I should tell you that I have a Macbook with the multitouch touchpad. I do not use the back-button in the browser, but I use a double finger swipe to go back. And that is the cause of the problem. When I use the back-button, the page reacts like expected. The popup appears before leaving the page, and I choose to leave or stay. When I use the swipe, I go back to the previous page, and then the popup appears. If I choose to leave, no problem. If I choose to stay, then the page turns white. The same happens when asking a new question. Writing a comment doesn't cause any issues.