Firefox 5 / Firefox 6 / Firefox 7 / Firefox 8 / Firefox 9 / Firefox 10 - javascript confirm/alert box freeze

I have exactly this problem:
support.mozilla.com - Firefox hangs sometimes on javascript "confirm"

A workaround is to change the appearance of javascript alerts:
support.mozilla.com - Change appearance of javascript alerts
short: go to 'about:config', search for 'prompts.tab_modal.enabled' and set it to 'false'. done.

This way the boxes come with a os-dependent style instead of the nice 'fade out' FFox5 style, but they do work again ;-)
Here is a site where you can test it: JavaScript Confirm


Just for reference, i'm using:
Mozilla/5.0 (X11; Linux i686; rv:5.0) Gecko/20100101 Firefox/5.0 Iceweasel/5.0
on a debian unstable/sid.
Update:
Problem persists on
Firefox:Mozilla/5.0 (X11; Linux i686; rv:6.0) Gecko/20100101 Firefox/6.0 Iceweasel/6.0
Update2:
Mozilla/5.0 (X11; Linux i686; rv:6.0.2) Gecko/20100101 Firefox/6.0.2 Iceweasel/6.0.2
Update3:
Mozilla/5.0 (X11; Linux i686; rv:7.0.1) Gecko/20100101 Firefox/7.0.1 Iceweasel/7.0.1
Update4:
Mozilla/5.0 (X11; Linux i686; rv:8.0) Gecko/20100101 Firefox/8.0 Iceweasel/8.0
Update5:
Browser version info like above; debian package version: 8.0-3+b1
Update6:
Mozilla/5.0 (X11; Linux i686; rv:9.0.1) Gecko/20100101 Firefox/9.0.1 Iceweasel/9.0.1
Debian Package: 9.0.1-1
Update7:
Wow. still not working. Might be a problem at my side.. whatever..
Mozilla/5.0 (X11; Linux i686; rv:10.0.2) Gecko/20100101 Firefox/10.0.2 Iceweasel/10.0.2

edit:
Added update for new Browser Version.
Changed Title (added "Firefox 6").
edit2:
Added update for ffox 6.0.2.
Added link for testing.
edit3: (07.10.2011)
-Updated info for FFox 7.0.1
-Changed Title (added "Firefox 7").
edit4: (25.11.2011)
-Updated info for FFox 8.0
-Changed Title (added "Firefox 8").
edit5: (17.12.2011)
-Updated info for FFox 8.0
-new sub-update (debian-specific)
edit6: (03.02.2012)
-Updated info for FFox 9.0.1
-Changed Title (added "Firefox 9").
edit7: (06.03.2012)
-Updated info for FFox 10.0.2
-Changed Title (added "Firefox 10").