Write a WebExtension that behaves correctly on both Firefox and Chrome, handling API namespace and background-context differences
domain: developer.mozilla.org · 6 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Use the browser.* Promise-based namespace as the primary API surface, matching Firefox's native model
Bundle Mozilla's webextension-polyfill so browser.* calls also work under Chrome's chrome.*-only implementation
For Manifest V3, check each browser's current 'background' manifest key expectations rather than assuming Chrome's service-worker model applies identically to Firefox
Register event listeners synchronously at the top level of the background script so they survive suspension/restart under either model
Persist state via storage APIs rather than in-memory globals, since the background context can be killed and restarted
Cross-check MDN's 'Chrome incompatibilities' and cross-browser extension pages before relying on any one vendor's behavior
Known gotchas
Firefox's MV3 background execution model is not identical to Chrome's — treat MV3 support as per-browser rather than a single unified spec
The webextension-polyfill smooths callback-vs-Promise and namespace differences only; it doesn't guarantee full API or manifest-key parity
Some manifest keys and APIs remain browser-specific, so verify against MDN rather than assuming Chrome's docs apply unchanged
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