Interesting, but not an OS exploit
"The rogue link remains even after the user copies a new batch of text. The only way to remove it is to reboot the computer."
That the problem can't be resolved by less drastic means, such as logging off, user switching, or killing the offending process seems... unlikely. In fact, according to at least one poster, they solved the problem by killing the firefox process. I suspect that the attack works by running a loop which continuously inserts the malicious link into the copy and paste buffer. This is supported by another poster reporting that they can, in fact, copy and paste another block of text, assuming they do it very very quickly.
If I had more time today, I'd fire up a virtual machine and go looking for a copy of this exploit myself; it looks like it would be fun to disect.