tl;dr: Browser Use rebuilt its cloud browser infrastructure on Firecracker microVMs running nested inside regular EC2 (rather than bare-metal), cutting session start times to under 1s and costs from $0.06 to $0.02/browser-hour. Key optimizations included using 2MB memory pages and a custom userfaultfd handler to slash page faults 91x, dynamic vCPU pinning after Chromium launch, and a Chromium fork with real fingerprints enabling fully headless stealth (81% block-avoidance). Next up: snapshotting VMs after Chromium is already running to eliminate the remaining ~545ms startup cost.