Dundee utd in Dundee, Hibs in Edinburgh, even in England, Everton was traditionally the catholic club in Liverpool and Man utd in Manchester. I'd say Glasgow remained the most bitter one on account of its close links to Ulster. If you read about Irish navvies working on the canals and the railways in Britain it was in Scotland that they were the most disliked and where the most violent incidents occured. Even today a lot of scots seem to be anti irish. You see it to a lesser extent in Liverpool as well if you scratch the surface of some people.

I'm not that strong on this aspect of history, but it has always seemed to be an association rather than a sectarian divide. Even though it was well known Everton was the catholic club, plenty of catholics supported Liverpool from the beginning, for instance. Glasgow and surrounding areas seemed the strongest exception.

You're right about sentiment in Liverpool though. That probably stems from the port and strong association as the point of migration leading to a large Irish community.