manifest-v3-test-surface-reference

Overview

Manifest V3 (MV3) is the current packaging contract for Chromium-family browser extensions; Firefox supports it as a peer with a documented divergence list. The manifest is the only declarative input both browsers see - every test surface (background lifecycle, permission prompt, content-script injection, web-accessible-resource fetch) hangs off a manifest field. Knowing which field maps to which runtime behaviour is what lets a test author decide whether a behaviour is testable in unit, integration, or full-browser scope.