+++ This bug was initially created as a clone of Bug #1700101 +++

Bug #1700101 comment#23, I filed this bug.

STR:

1. Click on the Library icon from the toolbar.
2. Click on the History option.
3. Rapidly close the panel via "<" button from the sub panel.
4. Repeat steps 2 and 3, if the issue is not reproduced instantly.

Actual Results:
The Library panel is broken.

OR
STR:

1. Put Text Encoding toolbutton in Overflow Menu.
2. Open data:text/html;Shift_JIS,Other than UTF-8:%E3%81%82<a href="https://www.google.com" style="float:right;padding-right:50px;">Go to Google</a>
3. Click Overflow Menu button.
4. Click Text Encoding to open sub-view.
5. Click < button at the top-left corner of the menu

Optionally
6. Once after this bug happen, attempt to click Go to Google link.

Actual Results:
This bug appears[step.5].
Once after this bug have happened, The Overflow Menu is always broken.
And the link is not responding[step.6]
Screencast: https://youtu.be/V-8EIxgG6s8?t=26

On Nightly89.0a1, when gfx.webrender.software.unaccelerated-widget.allow is false it's possible to hit a similar issue, but it's much much more rare.

Possible regression window:
Because it is rare to reproduce the problem. More trials may be needed for GOOD builds.
At least in BAD builds, the problem can be reproduced.
Bad build:
BuildID=20200213214257
SourceRepository=https://hg.mozilla.org/mozilla-central
SourceStamp=51dbdcd6e874c5d466f7a163e43973358e06284d

Jim, could you evaluate the severity and severity of this bug? Thanks