firefox complains about glxtest: Unable to open a connection to the X server via vnc

+++ This bug was initially created as a clone of Bug #2035207 +++

Description of problem:
firefox complains about glxtest: Unable to open a connection to the X server via vnc

Version-Release number of selected component (if applicable):
firefox-91.4.0-3.el9.x86_64

How reproducible:
always

Steps to Reproduce:
1. start vncserver
2. firefox --display=:1
3.

Actual results:
Running without a11y support!

(firefox:66960): Gtk-WARNING **: 03:59:05.581: Locale not supported by C library.
Using the fallback 'C' locale.
Crash Annotation GraphicsCriticalError: |[0][GFX1-]: glxtest: Unable to open a connection to the X server (t=0.215207) [GFX1-]: glxtest: Unable to open a connection to the X server
Crash Annotation GraphicsCriticalError: |[0][GFX1-]: glxtest: Unable to open a connection to the X server (t=0.215207) |[1][GFX1-]: glxtest: libEGL initialize failed (t=0.215239) [GFX1-]: glxtest: libEGL
Fontconfig warning: ignoring UTF-8: not a valid region tag

Expected results:
firefox renders webgl content such as https://collinhover.github.io/kaiopua/

Additional info:
firefox starts up and seems to work ok, except that it really doesn't render webgl content despite webgl.disabled = false