I was noticing that on some websites (forums), the cursor was not displaying correctly in text boxes. It doesn't animate (flash) correctly, and is invisible most of the time, thus making editing text extremely difficult.
This forum for example: http://www.overclock.net/ - if I go to post a new topic or reply, the cursor will be bugged.
I discovered that this only happens when the 'Shockwave Flash Object' Add-On is enabled. Disabling it resolves the issue, but obviously I would like to retain it's functionality for viewing embedded flash videos etc.