Shameless plug: If you're interested in this functionality, but want it in all browsers without needing any plugins, check out my start up BugMuncher - https://www.bugmuncher.com
It's also worth mentioning that because BugMuncher uses a big farm of Selenium servers, it's pretty rare that it can't take the screenshot in the exact same Browser / OS as the user. And in those scenarios, BugMuncher uses a scoring algorithm to find the closest match available.