A friend here at
Knackeriet is developing a tool to find
UI bugs by taking screenshots across many different browsers. It's called
Happo.io.
In the past I used Browserstack to make sure that frontend changes I made on my websites didn't break the design in different browsers. But that was very time consuming, and sometimes visual bugs could still slip through.
Happo generates screenshots of selected segments of a webpage, and all the visual changes are reported, and can be easily compared with the original segments. That makes the whole experience of doing frontend changes to a website a lot smoother.