Flyspray

Encountered the same thing, a co-worker noticed about it. Seems that something has changed in Firefox, it was working properly in last spring. Did some testing and it still works with IE 11 (Windows 7), Edge (Windows 10), and the remaining on Kubuntu 15.04: Chrome 45, Opera (can't remember version number, the latest one, don't have it installed home) and Rekonq 2.4.2. Have to test what happens if I comment out line 5466 in prototype.js.

Is failing in firefox and Alpha 2
Something to do with onmouseup="Event.stop(event);" ??

Yea, I think the same.

I wanted replace the key listener event and replace it by pure css toggle for hide/show of closing form, but got a veto from psycho. Maybe I can convince him this time?
Maybe to emulate his 'click everywhere to close the popup closing form' by a underlying fullpage label..

The problem definitely is Event.stop(event). Here's the definition of it (in prototype.js):

  function stop(event) {
    Event.extend(event);
    event.preventDefault();
    event.stopPropagation();

    event.stopped = true;
  }

Firefox as the only browser now actually implements preventDefault() correctly (in my opinion), so it prevents the selection from happening. Did some testing with a few different browsers again (Edge omitted, don't have it available here at home), and it seems that replacing it with onmouseup="event.stopPropagation();" should be enough to prevent the event bubbling upward also to project selector. I think that was original problem that the onmouseup event handler tried to prevent (it really happens if the event handler is removed). But waiting for a comment before making a pull request.

We were not the only ones with this problem.

https://bugzilla.mozilla.org/buglist.cgi?bug_id=1194316,1195675,1196390,1196486,1197347,1197533,1197655

But it is now fixed by Jouni in Flyspray source, and in Mozilla Firefox with Version 40.0.3..