The original bug is about "support installing 1.5.0.x back over 2.0.0.x (after a major update)". Thanks to rob strong for pointed out this variation. r=rstrong, sr=dveditz, a=dveditz git-svn-id: svn://10.0.0.236/branches/MOZILLA_1_8_BRANCH@220130 18797224-902f-48f8-a5cc-f745e15eee43