This has been happening to me for a while now, I just haven't done anything about it until now.

This is a recurring problem that I can reproduce. Iceweasel freezes whenever I try to upload a file (like a picture) to a website.

Now, I usually run iceweasel with krunner (the dialog, used in a launchy-like context) in KDE4. I recently tried running iceweasel from the console to view the error messages that I get when I try to do this, and the problem disappeared. So there is only a problem when it is run from krunner. I don't know if the problem is with krunner, iceweasel, or perhaps a java/flash upload problem.

I've done some searching and haven't been able to find any information on this anywhere. Is anyone else having the same problems, or does anyone know a solution?

iceweasel 3.5.5
KDE 4.3.2, Debian Sid

Some sites have a java applet that opens to upload a file. Make sure you have java runtime installed. One site I use also has a link to click that allows 'manual' upload. Check to see if the site allows that. Also try right clicking the upload link and check the properties to determine what type of application is used for uploading files.