Check if we are missing getCompatVersion in some places in the updater

One of the mechanisms we use for the updater is to use our version, instead of Firefox's, to issue updates to patch other bundled components, such as tor, PTs, or simply to update some prefs (e.g., domain fronting).

So, in toolkit/mozapps/update/UpdateService.sys.mjs we often replace Services.appinfo.version with getCompatVersion(). However, there are some places where Firefox's version is still used, e.g.,

        updateIsAtLeastAsOldAs(
          lazy.UM.internal.readyUpdate,
          Services.appinfo.version,
          Services.appinfo.appBuildID
        )

We should check what this implies.