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