I can understand that the state of the advertising market is such that these things might be necessary but I'd buy a premium membership just for the option to turn the sidebars off entirely.
Might not help for the mobile version, but I've hacked up a quick GreaseMonkey
script, downloadable here
. Install the GreaseMonkey plugin, save the file as untwittrekbbs.user.js, open in firefox, and you get to enjoy the BBS in wide-screen glory once again.
Thanks! That worked perfectly. My point remains, though, I'd prefer to be able to turn it off without using a script.