Since bug 429023 we can set spellchecker.dictionary_path via about:config or a systemwide prefs file in browser/defaults/preferences/. Thing is, if that var is set, *only* the dictionaries from that dir will be loaded, and not the en-US one... I think it should add that dir to the bundled /dictionaries/ dirs list for completeness.. probably a logic bug with an else in the codepath changed by bug 429023.

Isn't that the intention? See bug 429023 comment 22 and the previous discussion.

Right.. im not sure i agree with the reasoning now, but adding another knob for that would be quite insane. Ian, Mike, you still think that's not a bug to not show the default bundled dict ? In that case i'll have to adapt to make sure a systemwide en-US dict is installed (which might not be as up2date, etc..)