Not 100% certain if this is related to the latest testing update or not but everytime I launch thunderbird now it Fc after 10 seconds with the following error
Exiting due to channel error.
Exiting due to channel error.
Exiting due to channel error.
Segmentation fault (core dumped)
edit.
It appears it Fc everytime I open a pdf attachment, if I manage to close the open pdf tab before thunderbird fc then it will work fine until I open another pdf attachment