If you'd flipped any graphics flags in about:config, system reboot was probably overkill (unless you'd updated system drivers too). Most likely just needed to

If you'd flipped any graphics flags in about:config, system reboot was probably overkill (unless you'd updated system drivers too). Most likely just needed to restart Firefox. But glad you got it working. And yeah, both Chrome and Firefox on Linux can be rather finicky with graphics cards due to high levels of unreliability in the past. Although the situation has improved over time.