Firefox in Ubuntu 18.04 had a special patch to enable global menu, which was dropped in subsequent versions.
I want to install that version in 20.04. One way to do this is to grab the .deb file and run
sudo apt-mark hold firefox. But then, I will have to manually apply an update when a new version is released.
Is there a way to configure
apt so that only firefox will be installed (and updated) from 18.04 repositories, while all other software will be installed from 20.04 repositories?
(Although the global menu patch was dropped when Unity was discontinued, global menu is very much alive due to KDE Plasma's global menu feature).