Specifically web links from thunderbird (78.14.10). I have no problem with my stand alone machine (and cannot replicate this issue/fault in a vm in my machine) even though both stand alone machines (mine and wife's) are running identical Desktops and versions of software. Wife's machine is running Mate 20.04 ( up to date) with firefox 93.00 and Apparmor 2.13.37 - everything has been installed via Synaptic (on both my machine/vm and wife's machine). What happens on her machine is .... if you click on a web link in an email firefox launches with a window including her normal bookmarks in the bookmarks toolbar (i.e. it looks like her unique version of firefox). However, ff is totally unresponsive, you cannot enter a url, you cannot type things like about:config in the address bar and there is no drop down menu if you click on file, edit, help etc. Totally dead. I have looked in /.mozzilla and no new profile is created - just her normal profile is present. However, if ff is running in the background when you click on a web link in tb then ff launches displaying the web page (as it should do). This sequence of events happens only when apparmor is installed. If I uninstall apparmor and restart then clicking on a web link in an email launches ff normally to the web page. I have disabled apparmor via sudo systemctl disable apparmor but this 'fault' is still present. It doesn't matter whether appamor is installed on its own or with all the profiles - the only way for this machine to operate normally is for apparmor to be uninstalled. As far as I can tell both machines are identical but there is obviously a difference somewhere. (I have reinstalled the software on her machine so I need some help as I'm not sure what to do next). As a temporary measure I have uninstalled apparmor on her machine but would rather have it installed for the extra security it offers/