System preferences not persisting

Hello.

It is very nice that Mozilla keeps the preferences separately so that 
they will be still there after a reinstallation. Unfortunately, there 
are some settings that do not seem to persist and it is annoying to have 
to manually reset them every time I install a new nightly (i.e. every day).

The settings in question are those under Preferences > Advanced > 
System. I do not want Mozilla to handle JPEGs, GIFs, PNGs and any other 
kind of image files, as I have ACDSee for that. And, on the same pane, I 
also make sure to uncheck the "Alert me if other applications change 
these settings" option. As soon as a reinstallation is complete, 
everything is selected again.

Is there any way to work this out? Does anybody know if there is a 
respective bug?

Thank you,

-- 
Ney André de Mello Zunino