I switched to modular x.org 7.0 on amd64. Almost all dependencies to <=xorg-x11-6.9 could be solved by unmasking newer versions of the specific packages, but even the newest available mozilla-launcher 1.4.5 wants to install virtual/x11 and x11-base/xorg-x11. Synced an hour ago.
*** This bug has been marked as a duplicate of 120320 ***