Question: Internet Explorer 9 was released today, and I decided to check a few Magento sites we build in the last couple of months to see if everything continues to work with the new version.

But unfortunately it doesn't. I came across one particular problem that is caused by the version of the prototype library which is shipped with Magento, version 1.6.0.3.

It looks like the cancelling events in eventhandlers isn't working.  

For example, if you try to log in to a Magento shop, and just leave the login and password fields empty, IE9 submits the form even if there were errors, and the errors disappear after the refresh.  

So that's quite a big problem I think.

So my question is: how can we deal with this problem? I see a couple of ways to deal with this:

* Wait for Magento to release a new version with fixes
* Upgrade the prototype library to the latest version which probably already has fixed the issue
* Mess around in the existing library and try to fix the bug in there

Waiting for a new Magento release isn't a good idea because it probably will take a few weeks before there is one, and because it will cause a whole lot of other problems if you are running a very old version of Magento.  

Upgrading to the latest prototype library is probably the best idea, but will everything in Magento continue to work with the latest version of prototype, does anybody has any experience with this?

So what's everybody's opinion about this problem?
Any ideas other than mine?

Answer: 
As upgrading Prototype has the potential to break a lot of things in Magento (and, honestly, doing *anything* in Magento has the potential to break a lot of things in Magento), I created a theme override for my

`app/code/design/frontend/{package}/{theme}/template/page/html/head.phtml`

file and slapped the following as the first element under the head tag:

`<meta http-equiv="X-UA-Compatible" content="IE=8" />`

This tells IE to pretend as if it is IE 8, where possible. This solved an issue where, for example, you could not check out and complete the payment process if you only have one payment method enabled, as in IE 9 the fields will all be grayed out.

Note that it really must be the first tag underneath the `<head>`.

Since upgrading Magento in any way has the potential to cause problems, I feel this is the least intrusive way to solve the issue in the near term.
As a quick fix, I think I would take the same approach you are advocating, and upgrade Prototype to a version that does not contain this issue. However, Magento will be coming along with a patch (this is too big to ignore), and at that point, it would be wise to undo your changes and apply the patch they provide to keep in line with normal upgrades.

It is rarely worth it to manually dig in the internals of Magento's JS, so that option seems a bit off to me. There are probably several places where this semantic is used and you may miss some of them.

Hope that helps!

Thanks,
Joseph Mastey