Script Summary: This script fixes the issue in Firefox 5, where the Facebook Chat 'hides' behind the main page.
I use Facebook Chat a lot, and in Firefox 5, the chat always 'hides' behind the main Facebook page when not in use.
This script simply changes the opacity of the chat to 1 when not in use, sop the chat is always above the main FB page.
See this image for an example of the issue this script fixes.
If this script doesn't work for you, contact me and I'll se what I can do.