@utu

I wrote in my first message a workaround of the problem (Gdk-WARNING **: XID collision, trouble ahead)
I made a small shell script containig:

nohup iceweasel 1>/dev/null 2>&1 &

and then modify your iceweasel.desktop in /usr/share/applications

The line Exec=
should be
Exec=sh path-to-shell/filename.sh

You will not get anymore error messages from iceweasel including XID collision error. You should know though, when you update iceweasel you will have to edit iceweasel.desktop again, or you can just copy it before you update and restore it after the update.