Thanks for the debug log, it does confirm the problem is related to the Windows Font Cache service.

The fix I mentioned earlier only applies if the Windows Font Cache service is set to the disabled state, in which case Sandboxie will not try to start it. But in your case you say the Windows Fon Cache service is not disabled, however it refuses to start for some reason.

I don't think the service is supposed to stop automatically, at least it has never behaved this way for me. You might have some problem with this service in your Windows computer.

But that is beside the point because obviously Firefox outside the sandbox is ok with the service not running. I'll change this part of Sandboxie again so it gives up trying to start the service after a couple of attempts. I'll have this in the next beta version.

For an immediate workaround, set the service to disabled, which will cause Sandboxie (version 3.58 and later) to not try to start it at all.

thanks tzuk. Disabled the service and now firefox runs perfectly in sandbox.

Should be fixed in version 3.59.03.