A few days ago, a test against the home page for cookpad.com revealed a float drop error in Firefox 3, in their main promotion of a user recipe. Since then, the recipe featured has changed, and thus the bug does not occur any longer.
But, this demonstrates an important point: if your site features user-generated content, you must be very strict with your presentation layout, because users may contribute content in shapes and sizes you never considered.
We believe this is one of Browsera’s core strengths, its ability to quickly validate hundreds of web pages and automatically detect problems. Performing a test like this manually against a large number of web pages takes too long and is too error prone.