Unfortunately it's not that simple. IE is used for rendering any HTML content on a Windows machine. The kernel of IE is used in any window you open to browse your computer, for instance.
Note that this vulnerability is an exploit that can be leveraged if you go to a vulnerable site. Do not open any strange emails or click on pop-up windows, and you'll generally be okay. Your best bet would be to use a browser that utilizes its own execution environment such as Firefox or Chrome, as you can be assured that neither one of them is using Windows kernel hooks to render HTML content.
FWIW, disabling Flash will not fix this issue. It's a code exploit in the IE framework, not an extension vulnerability.
That is simply not true.
There is a really simple way to test this. Go to the Acid Test site with Firefox, Chrome, and IE. You'll notice they all handle the tests differently. All microsoft programs may well use the IE rendering engine for displaying HTML, but other programs do not. You can get a plugin for FF that will let it use IE, but by default it does not.