My firefox profile was on another disk partition than /home (because it is shared between several OS).
I have copied it into the ~/.mozilla folder and then there's no bug anymore !
So the bug it has nothing to do with the content of the firefox profile but it depends on the path to the firefox profile.
So when working with passwords, libreoffice does read the profile.ini file in ~/.mozilla folder (WHY?), then :
- if the path to the profile is not relative and situated outside the ~/.mozilla folder -> bug
- if the path is relative and inside the ~/.mozilla folder -> NO BUG