[Proxmox] Sometimes Firefox starts with a blank/black screen

[cliffe]

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When Firefox autostarts while KDE is still booting, it starts with a black screen. Closing then re-opening Firefox fixes it. Would be better if we fixed this.

Possibly not caused by SecGen code, maybe our base-box needs configuring to disable hardware acceleration, as per: https://support.mozilla.org/en-US/questions/1026178