Do firms still attach much weight to a college being an Ivy League college compared to another college which is of equal rank but is not Ivy League? or do firms attach most importance to ranking?

My impression is that in undergraduate education Ivy League status still carries some weight, but as far as law schools are concerned, that grouping has no meaning whatsoever. Stanford Law School is as good as it gets, despite not being in the Ivy League. Same goes for Chicago. Ivy League is mostly history, I think.

The Ivy League is a college sports league established in the 1950's consisting of most of the precolonial US universities (and Cornell which is quite a bit younger). see www.ivyleaguesports.com

College sports is primarily an undergraduate thing, and whether a university is a member of the Ivy League should therefore be of marginal importance(if that) in your choice of law school (of the top 6 law school 3 are Ivies and 3 are not).

If you are into college sports Stanford - a non-ivy - is, by the way, clearly the better of the 6.