Ergänzung meiner Fehlerbeschreibung (vielen Dank für die Nennung der weiteren Schritte in der Fehleranalyse):
1. Test mit Live Ubuntu 20.10 und dem darin enthaltenen Firefox 81.0.2 (64 Bit) brachte keinen Fehler
2. Parallel nutze ich Manjaro-Linux Ornara 21.0 mit Firefox 87.0 (64 Bit), auch dort ist Firefox fehlerfrei
3. Terminal-Ausgabe:
lspci -nnk | grep -A3 "\[03..\]:"
01:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] RV710/M92 [Mobility Radeon HD 4330/4350/4550] [1002:9552]
Subsystem: Dell RV710/M92 [Mobility Radeon HD 4330/4350/4550] [1028:0415]
Kernel driver in use: radeon
Kernel modules: radeon
4. Terminal-Ausgabe:
xrandr --prop
Screen 0: minimum 320 x 200, current 1366 x 768, maximum 8192 x 8192
VGA-0 disconnected (normal left inverted right x axis y axis)
TearFree: auto
supported: off, on, auto
scaling mode: None
supported: None, Full, Center, Full aspect
load detection: 1
range: (0, 1)
link-status: Good
supported: Good, Bad
CONNECTOR_ID: 46
supported: 46
non-desktop: 0
range: (0, 1)
LVDS connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 309mm x 174mm
_MUTTER_PRESENTATION_OUTPUT: 0
EDID:
00ffffffffffff0006af3c2100000000
01130103901f11780a09e59757549327
22505400000001010101010101010101
010101010101201c5680500023303020
360035ae1000001a201c568050002330
3020360035ae1000001a000000fe0054
50334852804231343058573200000000
00000000000000000001010a20200057
TearFree: auto
supported: off, on, auto
scaling mode: Full
supported: None, Full, Center, Full aspect
link-status: Good
supported: Good, Bad
CONNECTOR_ID: 48
supported: 48
non-desktop: 0
range: (0, 1)
1366x768 60.02*+
1280x720 59.97
1152x768 59.95
1024x768 59.95
800x600 59.96
848x480 59.94
720x480 59.94
640x480 59.94
HDMI-0 disconnected (normal left inverted right x axis y axis)
TearFree: auto
supported: off, on, auto
audio: auto
supported: off, on, auto
scaling mode: None
supported: None, Full, Center, Full aspect
dither: off
supported: off, on
underscan vborder: 0
range: (0, 128)
underscan hborder: 0
range: (0, 128)
underscan: off
supported: off, on, auto
coherent: 1
range: (0, 1)
link-status: Good
supported: Good, Bad
CONNECTOR_ID: 50
supported: 50
non-desktop: 0
range: (0, 1)
5. Dieser Fehler tritt nur im Firefox auf. Alle anderen Programme laufen einwandfrei. Als Browser verwende ich aktuell Falkon