Menu : Edit / Bookmark / previous and next bookmark have the same shortcut (ALT-P), so I can just move to the previous one.
The original shortcuts are Alt-PageUp and Alt-PageDown.
Now, either it doesn't display them fully for some reason (try them if they work), or keybinder has reconfigured them. In the latter case, remove keybinder*.ini (or temporarily disable it in Plugins->Manage to see if it is the culprit).