robzilla - 10:46 am on Aug 10, 2012 (gmt 0)

A stopwatch (or smartphone equivalent) is a poor measuring device. Both Firefox (with Firebug add-on) and Chrome (built-in Developer Tools) allow you to see what resources are loaded, and how long this takes. Compare those results, as well as the headers sent and received, and you might find the culprit.

If I recall collectly, Chrome is slightly better than Firefox in terms of Javascript performance. If your CMS is script-heavy, that might explain the difference.

It does not have to be a rendering issue, though. It could be that your CMS treats browsers differently.