In OS X, with full keyboard access turned on (In System Preferences, under Keyboard->Shortcuts, select All Controls), tab navigation in in-content-preferences is broken due to lack of focus feedback. One can actually tab to buttons, radio buttons, etc, but there's no indication that they're focused. Technically speaking, this happens because with -moz-appearance: none now set on all controls, the native focus rings are lost. I'm not sure what's the situation on on other platforms, but it's probably better because focus rings were never drawn "natively".

In conjugation with bug 1016169 (unfocused checked check-boxes and radio-buttons have focus rings), the UE is quite painful.

Note this also applies to the panes sidebar.