A family user of Lubuntu 18.04 has twice experienced a problem while using Thunderbird where, while dragging an email from the inbox to a local folder, if they mistakenly touch the panel with the cursor, it freezes the entire desktop. They didn't even drop the email on the panel, just touched it.

I confirmed this problem in a virtual clone of their system.

REISUB didn't seem to work. I can ssh in and restart the computer or kill Thunderbird to recover ops.

It only happens if the cursor touches the area of the panel to the left of the rightmost red marker. If it touches the running Thunderbird icon or anything to the right of it, it is OK.

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When it first happened, the friendly family IT guy (me) gave counseling "don't do that" but now it's happened again.

I'd like some protection against this happening again if possible or at least a single-user recovery method.

Addition: same problem happens on an 18.04 Ubuntu system with LXDE installed. So looks like a Thunderbird / lxpanel interaction problem.

  • 3
    Indeed. I can mostly replicate it here (I'm a big Lubuntu fan but stick with 18.04 as I'm not a fan of LXQt). I don't think you'll get a resolution, as LXDE is going to be left on the side of the road, discarded as though it is worthless. However, I was able to CTRL + ALT + F3, login w/user and password, sudo killall thunderbird, and then ALT + right arrow my way back to the desktop. I didn't try REISUB, as I didn't get that far.
    – KGIII
    Sep 20, 2020 at 19:07
  • 1
    @KGIII Thank you for the workaround. I'll give it a try. Sep 20, 2020 at 19:08
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    By freezes the entire desktop, is the mouse still working? I'd report on launchpad and maybe against package lxpanel (my 2c anyway). I don't use thunderbird, so added it to a Lubuntu 18.04 LTS and added a RSS feed (didn't want to setup mail), dragging a news.item around I was able to have the inputs (mouse & keyboard) freeze. My display kept updating (I had top in a window) and mouse moved over screen (though it remained in the display as if still dragging my news item around). The chances of a bug being fixed isn't great, but I'd still recommend filing (I didn't see any)
    – guiverc
    Sep 20, 2020 at 22:59
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    Nah sorry, I'm having second thoughts on my lxpanel, it continues to operate normally, even if it helped trigger the issue.. the killing of thunderbird fixing would be seen as reason to say wrongly filed... interaction between then causes a deadlock/hang.. and like @KGIII I don't see any stand out clues...
    – guiverc
    Sep 20, 2020 at 23:13
  • 2
    @guiverc you're right, I tried it on the Ubuntu + LXDE system and the mouse pointer would still move, and the gkrellm and conky displays showing behind the window kept updating. I agree the odds of getting anything fixed are slim, if LXDE had a future (sob) I might have pursued it. It doesn't happen in Ubuntu MATE which will likely be our next desktop. At least my family member can get out of the situation now without having to call me. Sep 20, 2020 at 23:59

1 Answer 1


Based on the comments:

I can confirm this bug exists and that it is repeatable. Lacking any error messages, the best solution is to not do it. If you do drag email and have this happen, it is possible to recover from it.

Open TTY with CTRL + ALT + F3.

Login by typing your username and then your password. Note, while typing your password, nothing will appear on the screen. This is normal and the expected behavior.


sudo killall thunderbird

Followed by pressing ENTER.

Repeatedly press ALT + (right arrow) until you return to your desktop, where you can restart Thunderbird and continue computing.

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