The 3.2 release of Facebook Tab Manager for WordPress adds support for the Timeline for Pages 810-pixel-wide tab layout introduced at the beginning of March. I had previously published some workarounds but this is the first update to bake support for the new tab layout into the plugin.
There is now a Tab Layout dropdown menu under options. For existing tabs, it defaults to the 520-pixel layout. For new tabs, it defaults to 810 pixels. Facebook Tab Manager sets this width on the HTML <body> tag for your tab content to prevent it from overflowing the width of the iFrame that contains it and causing scroll bars to appear.
When you record the parameters for your app in Facebook, you must also specify the 810-pixel width there. The new tabs (which Facebook now also refers to as “page apps”) also seem to require you to record the canvas URL parameters under “App on Facebook” in addition to the tab url parameters under “Page Tab.”
You should also take the time to edit the large icon associated with your app, which will be used as the source for the image used to advertise your tab on the Timeline.
You can see the results here. You can run this test yourself by creating a fbtab post containing the shortcode [fbtab_width_test]. Note that the border of the 810-pixel width box is clipped off because it’s right at the limits of the body width.