Hi
1.24.0.2 here but small correction (judging from what I see in my version):
In short; order of the window list applet is alphabetically A-Z and windows title is decided by active Firefox tab and thus window title of Firefox. It's not random (here at least).
If a window title changes while you're using some other application it will be somewhere else in the window list (still alphabetically though). Think of some youtube playlist, for example, where the windows title changes each video/song.
No way to change this as far as I can tell though, sorry.
Are you seeing different behavior? Can't tell from your screenshot...
I read something about thumbs being shown in the latest version so could very well be that you've encountered a bug of some sort.
Can't verify but worth mentioning I figured.
If it really seems completely random all of a sudden I would file a bugreport.
If you just want more sort options but the list is alphabetically I would file a feature request.