extension: support Firefox packaging and runtime

[wolf31o2]

ui/extension/public/manifest.json currently produces a Chrome-only Manifest V3 artifact. It declares only background.service_worker, which Firefox does not support, and the extension documentation and CI only load and exercise Chrome. In Firefox the background relay cannot start, so pairing and CIP-30 calls cannot work.

Required implementation

Build and manifests

• Keep one manifest source of truth. Either generate browser-specific manifests during the build or use one Manifest V3 manifest with both background.service_worker and background.scripts; do not maintain divergent hand-edited manifests.
• If one manifest contains both background keys, set minimum_chrome_version to at least 121. Set browser_specific_settings.gecko.strict_min_version to at least 128 because the required content_scripts[].world support starts there.
• Add a stable browser_specific_settings.gecko.id for Manifest V3 signing. Add browser_specific_settings.gecko.data_collection_permissions after tracing the data sent from dApps to the local Bursa service; do not default it to none without verifying the AMO classification.
• Keep background.js valid as both a Chromium service worker and a Firefox non-persistent event page. Do not depend on service-worker-only globals or in-memory state surviving background suspension.
• Produce deterministic, clearly named Chrome and Firefox packages with manifest.json at the archive root. The Firefox package must be ready for AMO signing; credentials and publication may remain separate release work.
• Add a pinned web-ext development dependency and repository scripts for Firefox linting and packaging. CI must run web-ext lint --warnings-as-errors against the packaged Firefox tree.

Provider and extension execution contexts

• Generalize extension: inject provider in the page main world #762 to both browsers: load injected.js directly in world: "MAIN" at document_start, and keep content.js in the default isolated world for extension API access and page/background message relay.
• Do not move the relay into MAIN; scripts there cannot use extension-only APIs and the page can inspect or modify their state.
• Remove the DOM-appended <script> and the injected.js web-accessible-resource entry once direct main-world registration is used. The provider must still load on a page with restrictive script-src CSP.
• Preserve origin checks, per-origin authorization, and token isolation. Pairing tokens and extension storage must never enter the page main world.
• Resolve extension: implement the CIP-30 provider contract #761 before declaring the Firefox provider usable by dApps; the same CIP-30 contract tests must run against both browser builds.
• Verify the current chrome.runtime and chrome.storage calls in Firefox. Introduce a small API wrapper or webextension-polyfill only where real-browser tests show that the existing callback/Promise usage is not portable.

Validation

Add automated tests using real Chrome/Chromium and Firefox instances. Do not use a DOM-only test as the Firefox acceptance test. Both browser runs must cover:

• unpacked/temporary installation without manifest or background-context errors;
• provider availability at document_start on a restrictive-CSP page;
• popup pairing with a local Bursa test backend and persistence of the token in extension storage;
• enable() approval followed by a successful CIP-30 request such as getNetworkId();
• deterministic unpaired, rejected-approval, and unavailable-background errors;
• background suspension/restart followed by a successful request using persisted state;
• no authorization reuse across different page origins.

Run the existing lint, type-check, unit-test, and build checks for both manifest outputs. Add a CI browser matrix and upload separate Chrome and Firefox artifacts. Update ui/extension/e2e/README.md with Chrome unpacked-loading and Firefox about:debugging instructions, the supported minimum versions, and the commands used to lint and package each artifact.

Acceptance criteria

• The packaged extension loads in the declared minimum Firefox version and current Firefox Release without manifest, injection, or background errors.
• A dApp can pair, enable the wallet, and complete a CIP-30 round trip through a running Bursa backend in Firefox.
• Restrictive page CSP does not prevent window.cardano.bursa from being registered.
• Chrome continues to pass the same provider, pairing, and authorization tests.
• CI publishes distinct Chrome and Firefox packages, and the Firefox package passes web-ext lint --warnings-as-errors.

References:

• Cross-browser Manifest V3 background scripts
• content_scripts[].world compatibility
• Firefox manifest signing settings
• web-ext lint, run, and build workflow