Does this still happen if you start Firefox in its Safe Mode? https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

Does the corruption linger after Firefox is closed, or is it only there when Firefox is running?

You can try to disable hardware acceleration in Firefox.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"

You need to close and restart Firefox after toggling this setting.

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

You can check if there is an update for your graphics display driver and check for hardware acceleration related issues.

• https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration