Browser warts
Microsoft has to keep IE going because so many enterprise customers still use it, with version six still being run internally for some processes, but it's a pain in the backside for Redmond because there's so much legacy code in there that the browser is sluggish and patching problematic.
That's what you get for winning the browser war and then sitting on your hands, muttering 'La-la-la! Can't hear you' for too long. I have no sympathy for them -- I'll reserve that for those of us who've had to live with their dull complacency and arrogance.