Comment 10 for bug 894085

I don't see that once set the setting being 'lost' when upgrading FF versions, though have to admit didn't pay close attention when FF went from 9.X to 10.X in 12.04

Definitely all new installs will have spell checking enabled but no language chosen, this is seen on Alpha 1 or any daily image. (& the need/means to pick a language isn't obviously presented to many users

As a quick test just booted to A1, ( FF 9). Spell checking was enabled but no language selected.
Selected a language & checked that spell checking now worked.

Then upgraded to FF 10, the language was still selected & spell checking still worked. This also included a log out/in after the upgrade in case that was a factor.

I guess this could be further checked by use of the firefox-next ppa on 11.10/04 & see what occurs when FF upgrades.