Serverless computing is a new paradigm that is rapidly gaining popularity in Cloud computing. One unique property in serverless computing is that the unit of deployment and execution is a serverless function, which is much smaller than a typical server program. Serverless computing introduces a new pay-as-you-go billing model and provides a high economic benefit from highly elastic resource provisioning. However, serverless computing also brings new challenges such as (1) long start-up times compared to relatively short function execution times, (2) security risks from a highly consolidated environment, and (3) memory efficiency problems from unpredictable function invocations. These problems not only degrade performance but also lower the economic benefits of Cloud providers. To address these challenges without any compromises, we propose a novel VM-level post-JIT snapshot approach and develop a new serverless framework, Fireworks. Our key idea is to synergistically leverage a virtual machine (VM)- level snapshot with a language runtime-level just-in-time (JIT) compilation in tandem. Fireworks leverages JITted serverless function code to reduce both start-up time and execution time of functions and improves memory efficiency by sharing the JITted code. Also, Fireworks can provide a high level of isolation by using a VM as a sandbox to execute a serverless function. Our evaluation results show that Fireworks outperforms state-of-art serverless platforms by 20.6× and provides higher memory efficiency of up to 7.3×.Published version