I notice that the System Details list shows you are using already the current release (86.0). Firefox downloads the update and prepares the new version in the updated folder and asks for a restart to apply the update (copy the files in the updated folder to replace the currently installed Firefox version). If you click this restart button then you close and restart Firefox, so no reboot necessary, but Windows might require a reboot if there is other (security) software keeps an handle (lock) on files in the Firefox installation folder. You can possibly save data you currently work on just to be sure before you click this restart button.