For details, see: https://wiki.mozilla.org/Fennec/Features/TabletUI
Thomas, I know we want the tablet changes in for Fx6 and that is why you made this bug a P1, but this bug is a meta bug. We need to make sure the dependent bugs we care about for Fx6 are tracking and prioritized.
*** Bug 653136 has been marked as a duplicate of this bug. ***
Adding the add-on compat keyword. Because mobile Firefox 9 has a whole new UI for tablets, any add-on that modifies or extends the mobile Firefox UI might need changes to work on tablets. For example, add-ons that place buttons in the right sidebar (id="controls-sidebar") should probably add those buttons to the appmenu instead. Add-ons may want to revisit their overall UI design too, to see whether it makes sense in the new tablet UI.
Add-on authors can run the desktop version of Fennec and enlarge its window to test in tablet mode. They can also set general.skins.selectedSkin=honeycomb/1.0 in about:config and then restart the browser to test with the Honeycomb theme.