A good idea this morning: download the last SpeedyFox (2.0.18) and optimize my Firefox (50.1.0). With trust, no profile backup...
But I was very wrong: at the next start, Firefox displays only a blank page, instead of the 2 windows with hundreds of tabs and hundreds of bookmarks. Then I made a copy of my profile.
Any idea? Do you need more information?
It broke compatibility with this addon: https://addons.mozilla.org/firefox/addo ... atibility/
If I disable it, all is back. I'm happy to have found this, but do you understand what happened?