You said you can make Internet Explorer faster by disabling add ons... and guess which one you say apparently uses too much memory? Your Bing search bar. I guess it's nice to hear when your very own products are considered badly coded by your web browser...
I hate search bars...they just seem like an excuse to advertise. But I can't say I'm surprised that Bing is causing issues...I've never been happy with IE itself in the first place. Both made by Microsoft, both "meh" products.
I remember hearing a few people say that there was a plug-in for Firefox that had a memory leak in it, and that Firefox itself also had a memory leak. I don't think this was Firefox 4, but yeah, I guess a lot of people have problems every now and then.
I hate Bing with a passion; it's just... annoying.