I'm back to comment on this thread and keep it alive. I know this is not the only thread about this. In Windows, the list functions do not work properly in the most popular browsers: IE, Firefox, Chrome. In Ubuntu, I believe Firefox worked for me once but I don't remember if it was 100% or partially. I have yet to test browsers on OS X.
Not a bug but a (return) feature request: Please put a button back on game pages to add to list. I used that all the time.
I tested today that in Firefox in Windows 7 64-bit, the buttons don't work. In Internet Explorer, the buttons do work but you get a red error bar at the top of the page upon submission. I booted into a live Linux DVD (Linux Mint 14 Cinnamon 64-bit with codecs) and used Firefox. Editing my lists worked perfectly!
I can't add or remove games from my lists via Firefox nor IE in Windows 7 64-bit. It really stinks. I converted from IGN years ago who did lists better at that time and had better game tracking. Game tracking is improved now. I'm looking forward to the lists at Giantbomb working again!
Not a bug, but I'm wondering where the "add to list" button is these days that was on the old site. That was much quicker to add games to my lists rather than browse to my lists, click on the list I want, then go into edit mode, then search for the game(s) I want to add.