Options keep resetting themselves to default, despite «Changes Saved» message showing?

[OwenAR]

Eg, for me «Enable GFM line breaks» is checked by default.
I keep unchecking it,
and "Changes Saved" flashes up in the top right corner,
but the setting doesn't stick
(ie, when I close the options tab and reopen it, it's checked again).

I also tested some of the other checkbox settings
(with both defaults, checked and unchecked)
and none of them stick either.

(
I installed it a while ago through Firefox's normal addon manager,
and the version is 2.13.1
)

[RealOrangeOne]

I too have this issue, but without the Changes Saved message.

Thunderbird 52.6.0, Addon 2.13.2, Arch Linux

incidentally, I also suffer from #447, but I don't think that's related