I've been using Google Chrome since mIRC 6.35 and something that has bugged me since that version (occurs in latest 7.1 as well) is that even if you un-check Activate Window under the Web Browser options clicking a URL in mIRC still activates Chrome.

Thanks for the bug report, I have replied to a related issue in this thread. As far as I can tell, there is no way to prevent the latest web browsers from activating their windows when a link is opened.