What is /Volumes/firmwaresyncd?
The firmwaresyncd system is Apple designed and expected to run at all normal boots. Perhaps the system didn't unmount it once the check was complete.

If you restart your Mac, I've not seen it stay mounted twice in a row, and if you get it always sitting, a support call to Apple might be in order to be sure your firmware is updated if you are running OS updates when asked to. I don't think it's cause for concern immediately, but making sure you would be prompted if you were out of date is a good thing to double check that your security and patches are up to date.