Firmware functional validation suffers from a series of performance limitations in practice, which in turn heavily relies on manual effort and becomes a major bottleneck of product time cycle. The requirement of repetitive run-time firmware execution for the validation environment demands novel techniques to accelerate the validation process. We propose an online firmware functional validation scheme utilizing the colored Petri net (CPN) model which can be generated automatically from the firmware source code. With simulation runs on the generated CPN models at run-time, the firmware execution path is presented and, if an error occurs, the location of error can be identified. An integrated validation tool has been designed and implemented to show the proposed validation methodology's potential and effectiveness. This tool is used in the validation of the universal serial bus (USB) initialization in unified extensible firmware interface (UEFI).