[qgis-qwc2] different results with different browsers

[Dr. Michael Hälsig]

Hi,
I have created a little app, which shows different results on different browsers. 

Debian: 
Firefox version 75 localhost:8081:  3 of 4 layers are displayed in the menu, from the QGIS Server on a real host only 2 layers are displayed and therefore selectable.
Chromium version 80.0.3987.162 localhost:8081 all layers are displayed and selectable, from the QGIS Server only 3 of 4 layers.
Opera version 67.0.3575.137 and Chrome version 83.0.4103.7 localhost:8081 and from the QGIS Server: all layers are displayed and selectable

Tablet & Windows 10 (newer hardware):
Firefox 68.7: all layers are displayed. 

This seems to correlate with the support of WebGL2 - in the Firefox console, where layers were not displayed, I found the message: "Failed to create WebGL context: WebGL creation failed: 
* tryNativeGL
* Exhausted GL driver options. 2 webgl.js:281:27"

Has anybody an idea, how to make Firefox show at least all layers in the menu? The reason cannot be the lack of graphics hardware, because Opera and Chrome display everything as expected. 

Thank you.

Michael Hälsig