Grazie per la risposa, ho provato safe-mode e mi compare: firefox -safe-mode
Xlib: extension "GLX" missing on display ":0".
(firefox:7437): Gtk-WARNING **: Theme parsing error: <data>:1:34: Expected ')' in color definition
(firefox:7437): Gtk-WARNING **: Theme parsing error: <data>:1:78: Expected ')' in color definition
Xlib: extension "GLX" missing on display ":0".
(firefox:7437): Gtk-WARNING **: Theme parsing error: <data>:1:34: Expected ')' in color definition
(firefox:7437): Gtk-WARNING **: Theme parsing error: <data>:1:78: Expected ')' in color definition
Xlib: extension "GLX" missing on display ":0".
Xlib: extension "GLX" missing on display ":0".
Xlib: extension "GLX" missing on display ":0".
Xlib: extension "GLX" missing on display ":0".
Xlib: extension "GLX" missing on display ":0".
(/usr/lib/firefox/firefox:7665): dconf-WARNING **: Unable to open /var/lib/flatpak/exports/share/dconf/profile/user: Permesso negato
[Parent 7437, Gecko_IOThread] WARNING: pipe error (123): Connessione interrotta dal corrispondente: file /build/firefox-pQ6x41/firefox-62.0.3+linuxmint1+sylvia/ipc/chromium/src/chrome/common/ipc_channel_posix.cc, line 353