This page is completely unusable due to lag. From the other comments it seems this is FF specific. One would think FB would have the resources to test new pages at least on common browsers before publishing.
Thanks for finding that out. We (Firefox) fixed a box shadow performance bug [1] in Firefox 47, which will be released on June 7th. It looks like this site is hitting that perf bug.
Completed nuked FF for me and for what its worth it doesn't even load in Edge. Just throws up a "This page is having a problem loading" page. Works fine in IE 11...
Edit: The fix came quickly though.