Check it out: Mozilla has made their crash reports available online. You can see crashes for all kinds of Mozilla apps, not just Firefox. But I think that the firefox stats are the most interesting. Here’s the top crashing domains for the last-but-one FF release (3.5.4). Here’s the top crashing urls for 3.5.4 (go FarmVille!). Here’s more about Firefox crash reporting in general (including links to the software that runs the online crash report server).
I’m not sure how useful this data is to normal web developers, since you can’t see if your domain is causing crashes unless it is among the top urls and/or domains in the trend reports. However, if you had a relatively high traffic website and you noticed, after a new FF rollout or new rollout of your webapp, that the FF user percentage had dropped off a cliff, you could try to see if your webapp was listed here with a large number of crashes.
Bravo for FF for releasing their crash data. I looked around, but didn’t see any academic research based on this data–I imagine you could find some interesting trends (checkins vs crashes per version, etc).