One of the most pervasive causes of crashes in Safari involves Adobe Flash content, in part because of the widespread use of Flash in banner ads. As reported by one poster to Apple’s Discussion boards, Espen S.:
“For the third time Safari has crashed while I was writing an email at Yahoo. The message that popped up after Safari disappeared stated that it probably had to do with the Flash plugin. The only update I have done, apart from Apples own, is to download and install the latest Flash player from Adobe (9.0.115.0).”
This creates a situation where Safari will seem to randomly crash in the middle of browsing as well.
Safari randomly crashes when running Flash content