The # symbol also is called a hash mark, and what followed it traditionally was a location in the page. However, sites also can use it to demarcate the end of the real address and the beginning of whatever information they want to keep track of as you move through the site. On Facebook in particular, a huge amount of stuff can pile up after the hash as you navigate.

Thanks for the reply. I'm just wondering why when I switch to Safari, it is not there? tonight I will pay attention and copy one for you. Thanks!

Such a hash symbol in a link is usually an indication that the link is created and handled by some JavaScript or script that runs on the server.\

Your older Firefox 3.6.x version may not be able to run such JavaScript properly and thus you see the link with the hash symbol instead of the result of AJAX calls with the hash symbol removed.
If the change happened recently then it is possible that the Facebook site updated their code.