From bug 1852790, the issue appears to be that the focal version was built before the eoan version. My current profile's compatibility.ini (from eoan):
[Compatibility] LastVersion=70.0.1_20191031091608/20191031091608 LastOSABI=Linux_x86_64-gcc3 LastPlatformDir=/usr/lib/firefox LastAppDir=/usr/lib/firefox/browser
vs. an upgraded profile's compatibility.ini:
[Compatibility] LastVersion=70.0.1_20191031000133/20191031000133 LastOSABI=Linux_x86_64-gcc3 LastPlatformDir=/usr/lib/firefox LastAppDir=/usr/lib/firefox/browser
You can see that the created-on-focal profile's LastVersion is about 9 hours older than the created-on-eoan profile's.
From bug 1852790, the issue appears to be that the focal version was built before the eoan version. My current profile's compatibility.ini (from eoan):
[Compatibility] 70.0.1_ 20191031091608/ 20191031091608 Linux_x86_ 64-gcc3 =/usr/lib/ firefox /usr/lib/ firefox/ browser
LastVersion=
LastOSABI=
LastPlatformDir
LastAppDir=
vs. an upgraded profile's compatibility.ini:
[Compatibility] 70.0.1_ 20191031000133/ 20191031000133 Linux_x86_ 64-gcc3 =/usr/lib/ firefox /usr/lib/ firefox/ browser
LastVersion=
LastOSABI=
LastPlatformDir
LastAppDir=
You can see that the created-on-focal profile's LastVersion is about 9 hours older than the created-on-eoan profile's.