test in win7 x64,safari 5.1.2,
a special png Optimized by PngOptimizer.exe in a "XHTML 1.0 Strict" doctype html will crash safari.
other browser,including,firefox 9,chome 15,ie 7,8,9,or safari,firefox and chrome in mac do not have this problem.
here is a demo html
if use html5 doctype "< !DOCTYPE html>",it will not happen either.