What are the (technical) pros and cons of Flash vs AJAX/JS?

Question

We provide a web application with a frontend completely developed in Adobe Flash. When we chose Flash 6 years ago, we did so for its large number of features for user interaction, like dragging stuff, opening and closing menus, tree navigation elements, popup dialogs etc.

Today it's obvious that AJAX/JS offers roughly the same possibilities and because of the number of frameworks that are readily available, it's very feasible to implement them.

Is there a technical reason one should choose either technology over the other? By "technical", I mean performance, security, portability/compatibility and the like. I don't mean aspects such as the very non-programmer way development is done in Flash or whether it makes sense to switch an app from one to the other.

As I just explained in another question, it seems to me that JS is way ahead in terms of market share and I'm wondering whether we are missing some important point if we stick to Flash.

Answer 1

In addition to what others have said, Flash is constrained in the "rectangle" and cannot be added to a normal html page in an un-obtrusive manner.

@Gulzar I think when more browsers will support the video tag like mozilla 3.1 does we'll see even more adoption of ajax/js over flash.