By "cross browser testing" I assume you mean the work was done and tested on some browser (The current version of Chrome) but you want to test on other versions and other browsers, possibly other platforms?
The problem here is the combination of devices and browsers and browser versions will keep you testing forever; you need to triage the work and the devices. Here's an article on how to do that that I wrote a few years ago for SearchSoftwareQuality:
http://searchsoftwarequality.techtarget.com/tip/Defining-a-strategy-for-...
good luck!
