Hello everyone.
I accidentally clicked on Thunderbird icon. Then this icon appeared on the Applet which contains all the types of notifications (unfortunately, I don't know how to translate that).
I typed sudo apt remove thunderbird, and this was successful.
I was trying to remove the icon from the panel, and finally I had installed dconf-editor. This didn't help me to delete the annoying icon, despite the fact I deleted Thunderbird from messages section.
Then I tried to xkill the whole panel, and there was no effect. I restarted it, and there was no effect!
I had opened MATE Tweak and set GNOME2 configuration (there was no other configurations).
Panel had disappeared. Desktop had disappeared too.
I typed sudo apt autoremove * gnome * (with no spaces around the gnome word, of course). There was some... strange package names which seems to be important (such as mate-terminal, but I deleted them anyway.
I typed in terminal: sudo apt install ubuntu-mate-default-settings, and get 0 packages installed.
I considered this OK, I thought "All the most important packages for my system are installed".
But there was still no desktop and no panel.
I had browser and terminal window opened. I found in the Internet that I should type sudo killall Xorg. Right after that command, my notebook shut down. Now I have infinite boot loop. What I should do?
P. S. Sorry for my English.
