This bug encompasses a number of installation/packaging changes related to enabling Versioned Installation Directory support (Bug 1891600). All of these changes should be gated behind the build flag that will be added in Bug 1891616.

There are a number of moving parts here, so I'm going to file sub-bugs for them.

To be clear, this isn't entirely just a metabug. I think that addressing the bugs dependent on this one will get us to the point where the (un)installer behaves properly. But we will need to make sure of that before we close this bug.

These are the success criteria:

• The installer should install using versioned installation directories when the installation directory is empty.
• The installer should overwrite an existing installation that doesn't use versioned installation directories.
• The installer should not overwrite any running installations when the existing installation does use versioned installation directories. Installations that are not in use should be removed.
• In all of the above situations, the Version Selection binary should be present in both the versioned subdirectory and also in top level of the installation directory, where it should be named firefox.exe. The copy at the top level should always be overwritten with the new version.
• The uninstaller should remove all installed versions.