I first thought of this as a problem with Firefox, so I started there. We built our Extjs application specifically for Firefox and Chrome, so when suddenly one could not log in with Firefox 12, it was a real problem for our users. And the Firefox upgrade announcement said that the upgrade was urgent and should be done immediately. So most people, seeing that, would upgrade, no question.
The Mozilla developers may fix this in version 13, if there are enough affected websites. More information can be found here:
or look at the bugzilla.mozilla.org exchange by searching for
Bug 749098 - cannot log in to website with Firefox v. 12.0
But the problem can be fixed on line 1010 of /modules/basex/ext-basex.js, as noted above. Our problem was: one filled in the log in information, clicked the button to login, the window disappeared and then immediately reappeared, instead of leading to the main application window. On the server, one could see the login attempt, and the fact that it went nowhere, but there were no errors on the server. And Firebug did not show any problems, either.