If these keys are handled by the OS, you're not going to get an event in IE.
You best option is to use something like Enterprise Browser that you can configure to capture all the keys.
I'm sorry but maybe I bad expressed for this request.
I do capture event key for F1, F2, F3, F4, F5, F8, F9 and F10 but I don't capture event key for only F6 and F7 because, I think that this key are associated at change text size.
I wanted know if the text size function can be deactivated in IE. Perhaps with reg file.