I'm developing and reviewing my prototype in FireFox and Chrome on the Mac. I'm using the prototype to conduct some informal usability tests, all done remotely using an online conferencing system. So I have don't have control over the platform used by my test subjects, and I've been noticing display inconsistencies during the test, which is not the best time to find these issues. The issue is: the text just about fits in the textbox on my screen (Mac- Firefox/Chrome), during development and review. On the test subject's screen (PC - IE/Chrome), the text does not fit and so is truncated and ugly little scrollbar elements appear next to it.
The only workaround I know for this is to make sure the textbox is longer than the text while I'm building the prototype, but since I'm working blind (no access to PC), it's not foolproof.