Browser Use details sub-second browser starts on nested Firecracker microVMs in EC2

Category: Engineering post
Status: confirmed
Sources: browser-use.com, discussion
Summary: Browser Use published an engineering write-up on 2026-06-15 on running Firecracker microVMs nested inside regular EC2 instances rather than on bare-metal, trading nested-virtualization overhead for faster provisioning and lower cost. Browsers resume from a VM snapshot paused just before Chromium launches, cutting initial restore from 9.8s to 3.1s. The team raised the guest page size from 4KB to 2MB and added a custom userfaultfd handler that preloads pages Chromium touches early, reducing page faults by about 91x. vCPUs are unpinned during launch then pinned to stable cores with real-time priority. A custom control plane handles fleet monitoring and placement without CloudWatch, and edge routers forward WebSocket connections to the placed VM. Reported metrics are VM cold start under 400ms, end-to-end browser creation at 825ms p50 and 1.35s p99, and cost cut from 0.06 to 0.02 USD per browser-hour.
Why it matters: The snapshot-resume, page-size, and userfaultfd techniques are concrete, transferable methods for cutting microVM cold-start latency in agent and browser-automation infrastructure.