Debian Tor Browser Showing a Black Screen

Answer form Debian bugs tracker : bug #942901

edit your /etc/apparmor.d/local/torbrowser.Browser.firefox and add the following line:

owner /{dev,run}/shm/org.mozilla.*.* rw,

Also add exactly the same line to /etc/apparmor.d/local/torbrowser.Browser.plugin-container. Then:

sudo systemctl restart apparmor

The Debian bug tracker states:

Message #5

Tor Browser 9.0 shows only black screens because the default apparmor profile does not allow write access to /dev/shm/org.mozilla.ipc.. like it does for /dev/shm/org.chromium.* and I was able to fix this issue by adding this workaround:

==> /etc/apparmor.d/local/torbrowser.Browser.firefox <==

owner /{dev,run}/shm/org.mozilla.*.* rw,