Thanks for all that info and the offer to do more testing. Hopefully other members having the problems will be able to provide their browsers / versions so that will help us narrow down the specific use cases. What makes things even more tricky is when people have plugins / extensions that also can cause problems.
You're quite welcome to any help I might be able to provide, as you've put a lot of time into makin' BYC such a good place to flock to ...
I rolled back each update like layers from an onion, testing both w/ and w/o add-ons, finding no scenario that did not prove IE9 stinks.
The issue is most probably not in your coding, but in that provided by Microsoft ... what a shock. IE7/8 require fonts to be in .eot format, but it seems IE9 still does not handle @font-face properly (I thought they 'fixed' that, but apparently not), and either it's the links which invoke javascript or those with select elements that causes the crash, most probably because IE9 fails to fall back to the default fonts (might check for 404 responses).
So, one workaround utilizes the smiley-face, but apparently any 2-bit character will do ...
... but, the following workaround
[edit] (
which I replace w/ another's, as the better of the two)
[/edit] seems to deal w/ yet *another* issue, in that IE's parser tries to load everything between opening/closing parenthesis as a single file, but throwing in a question mark causes IE to see all thereafter as a query string ...
One more thought is that listing numerous fonts has often exposed bugs. I recall times that trailing spaces before the comma caused problems, and not enclosing font names, or even enclosing them differently ('font name' or "font name") can possible make a difference. There's always the option to *not* import fonts, which I don't personally see as detrimental to the overall well-being of your website. For certain? It'd be a good way to isolate the problem (I usually copy the required files into a new directory, and test during lower traffic periods ~'-)
It's a shame you can't just follow 4ormat's model, but I'd bet my favorite chicken that the overwhelming majority of your users are Windows/IE ...
[edit] Android 2.3.4 w/ both default browser and Firefox -- no known issues.
Both Firefox 12.0 and 16.0.1 work fine. [/edit]