Speculation Rules Testbench door Sky Ning

Speculation Rules Testbench adds a dedicated panel to Firefox DevTools for investigating navigational prefetch behavior on real websites.

The panel can:

• find and classify inline Speculation Rules;
• identify list, immediate, same-origin prefetch targets supported by the
  Firefox Milestone 1 implementation;
• capture speculative and top-level request lifecycles;
• show Sec-Purpose, completion status, cache headers, cache hits, Navigation
  Timing, and deliveryType when Firefox exposes it;
• compare normal behavior with a control that blocks speculative prefetches;
• enforce a matching source/target pair and explicit cache isolation; and
• export a privacy-sanitized JSON report.

The extension is intended for browser engineers, performance investigators, and web developers. It is an investigation tool, not a performance benchmark: single runs should not be treated as statistically meaningful performance results.

Captured data remains in the local extension process. Nothing is uploaded automatically.