Why don't Microsoft allow customisation in IE?

I use Firefox for the majority of surfing, but am forced to keep IE for updates and opening e-mail attachments, etc. I actually don't mind IE7 - aside from the fact it's slower than Firefox - but my main issue is the lack of customisation available. For example, Firefox allows add-ons and themes, and you can effectively change the whole appearance of it.

So why don't Microsoft allow this in their browser? Does anyone know why they're so behind the times on this?

Why don't Microsoft allow customisation in IE?windows vista home premium

because microsoft thinks that their stuff is perfect, so why would people cutomize?

and they have no taste in UI (they need to learn some things from steve jobs)

Why don't Microsoft allow customisation in IE?ie tab internet explorer

Because Microsoft is a bureaucratic monstrosity. It's a miracle they can get anything done with so many chiefs and so few Indians.
They do, you just have to be able to know when to use "doesn't" instead of "don't."

I don't

They don't

We don't

He/she/it doesn't