Mozilla actually run the unit tests of most major libraries as part of their regular test suite to make sure that the Internet will by-and-large still work on any new release. So I think the author has a valid point here, new browsers shouldn't break existing libraries this badly.
Perhaps, but as the parent post had stated: the changes to JQuery were to get rid of workarounds for past versions of IE. If Microsoft kept bug-for-bug compatible with older versions of IE, they'd be lambasted for that. Now you're lambasting them for actually fixing things. Rock, meet hard place.
