Update Oct 2014: It was noted correctly in the comments, that Firefox has deprecated the synchronous setting in June 2014, but it is still working in this browser. Furthermore, Chrome received updates which will only allow this to work as wanted if the ajax call returns in less than a second. Which is rather hard … Read more
Yes, popups should be a direct result of a user action. Doing them in ajax callback will not do the trick. Also, using async:false is bad – in FF it is known to block the whole browser. Think of some other way to do the check: it could be the first thing you do in … Read more
The general rule is that popup blockers will engage if window.open or similar is invoked from javascript that is not invoked by direct user action. That is, you can call window.open in response to a button click without getting hit by the popup blocker, but if you put the same code in a timer event … Read more