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Browser compatibility

Peerd targets desktop Chromium and Firefox. This is the single durable ledger for browser-platform differences that cause a concrete loss of Peerd functionality or isolation. It is not a general roadmap or a claim that two browsers expose identical extension APIs.

Last audited: 2026-08-11. The packaged Firefox 149 Pod smoke rejected the raw blob module Worker before it executed; the ordinary shell/WASI/persistence checks passed. Firefox 154 sandbox support is an upstream milestone and has not yet been adopted or verified by Peerd. Upstream statuses below are snapshots; follow the linked issues for their live state. An upstream issue closing is not enough to remove a guard: the exit check in this file must pass in a packaged extension.

Current user-visible differences

Surface Chromium Firefox Classification
WebVM and threaded WebAssembly WebVM can boot in a cross-origin-isolated extension page WebVM cannot boot from an extension page; WebAssembly that needs shared memory/threads is unavailable. Non-threaded WASI in Notebooks and Pods is unaffected Blocked upstream
Pod JavaScript js runs Web-standard JavaScript in a sealed module Worker js is refused; the shell, OPFS, Git, HTTP bridge, and WASI remain available Platform behavior under review plus a Peerd guard
Apps Opaque-origin manifest-sandbox runner is available Unavailable in the current Peerd Firefox package Upstream fixed for Firefox 154; Peerd adoption pending
Headless/offscreen services Headless script/page_code, site-client and A2A code runners, PDF/document conversion, rich HTML extraction, voice/local-model hosts, and per-actor Worker heaps are available Those offscreen-hosted tools are absent or fall back; notably, bound actors fall back to the service-worker heap and lose the dedicated memory boundary Peerd architecture gap; upstream API request is WONTFIX
Advanced tab automation Preview/dev builds can use CDP; the store build uses the scripting fallback Uses the scripting fallback: core read/navigate/click/type work, but page_exec, trusted page_keys, cross-frame accessibility snapshots, and some hardened-site flows are unavailable Accepted fallback around a missing API

The side panel/sidebar naming difference is not a capability loss. Minor UI differences such as tab grouping are also omitted unless they begin preventing a user or agent workflow.

Upstream issue ledger

FF-COI: extension pages cannot opt into cross-origin isolation

  • Peerd impact: WebVM (CheerpX) cannot boot, and threaded WebAssembly cannot share memory with Workers from a Firefox extension page. This does not block ordinary WebAssembly or WASI Preview 1 commands.
  • Upstream: Mozilla Bug 1673477 (REOPENED) and the cross-browser proposal in WECG issue 1039 (OPEN). Mozilla tracks per-extension process isolation separately in Bug 1827085.
  • Peerd guard: Firefox packages strip the unsupported COOP/COEP manifest keys in packaging/gen-manifest.ts, and the WebVM preflight explains the limitation through firefox-webvm-note.js.
  • Exit check: a packaged Firefox extension page reports crossOriginIsolated === true, can transfer a SharedArrayBuffer to a Worker, and passes the WebVM boot and threaded-WASM browser tests.

FF-MV3-WORKERS

Dynamic Worker/CSP behavior is not yet a stable Firefox Pod contract.

  • Peerd impact: Firefox Pods refuse the js command. Shell commands, files, browser-native Git, brokered HTTP, and installed WASI commands continue to work.
  • Upstream: Mozilla Bug 1869152 (NEW) tracks inconsistent Worker behavior in Manifest V3 extensions, including blob Workers and extension-packaged Worker scripts. It is the behavior tracker, not a promise that Firefox will permit Peerd's generated code path.
  • Peerd guard: pod-tab.js refuses the dynamic module Worker on Firefox, and the packaged smoke in run-pod-smoke.mjs pins the honest error and directly probes the browser's raw blob-module-Worker behavior instead of silently routing to a weaker execution boundary.
  • Exit check: the final Firefox MV3 package can create the sealed blob module Worker under its shipped CSP, AMO policy permits the construction, and the same realm-seal, cancellation, egress, and red-team tests pass as Chromium.

FF-SANDBOX: manifest sandbox support landed in Firefox 154

  • Peerd impact: Apps are disabled because Peerd's current Firefox manifest strips the sandbox key and the runtime refuses to open an App without a proven opaque-origin runner.
  • Upstream: Mozilla Bug 1685123 is RESOLVED FIXED for Firefox 154.
  • Peerd status: this is no longer an upstream blocker. Peerd must decide when Firefox 154 is an acceptable minimum, retain sandbox plus its CSP in the Firefox manifest, and remove the Firefox-only App refusal.
  • Exit check: packaged Firefox App tests prove an opaque origin, no extension API access, no ambient network, correct Worker rewriting, and normal create/edit/preview/version/reopen behavior.

FF-OFFSCREEN: Firefox uses event pages instead of chrome.offscreen

  • Peerd impact: the headless tools and document/media/model hosts listed in the table are unavailable or degraded. More importantly, actor turns can fall back to the service-worker realm; the exact security consequence is documented as residual risk R1.
  • Upstream: Mozilla Bug 1807830 is RESOLVED WONTFIX; Mozilla's stated replacement is the DOM-capable MV3 event page. The cross-browser API discussion remains in WECG issue 170.
  • Peerd status: this is a Peerd architecture task, not something to wait for Mozilla to fix. The current gate is offscreenAvailable in service-worker.js.
  • Exit check: a Firefox event-page or equivalent host provides the same lifecycle, cancellation, keyless Worker boundary, and document/media capabilities, with Firefox browser tests covering both success and recovery.

FF-DEBUGGER: no compatible chrome.debugger extension API

  • Peerd impact: Firefox uses the same chrome.scripting/DOM-walk path as the initial Chromium store build. It cannot provide CDP-only trusted input, page_exec on Trusted-Types pages, or the full cross-frame accessibility tree.
  • Upstream: Mozilla Bug 1316741 remains NEW; the older direct Chrome-parity request, Bug 1241448, is RESOLVED WONTFIX.
  • Peerd fallback: the capability gate and exact fallback surface are in service-worker.js; the top-frame-only snapshot constraint is in walk-injected.js.
  • Exit check: Firefox exposes a reviewed automation API with the required trusted-input and inspection semantics, or Peerd implements equivalent behavior without weakening page or user security.

Maintenance rules

Update this file when a browser guard/fallback changes, an upstream issue moves state or milestone, or a packaged-browser test changes the verified result. For each entry:

  1. Keep the user-visible loss precise; do not write “Firefox unsupported” when only one execution path is missing.
  2. Link the narrowest primary upstream issue, not a project-wide issue list.
  3. Say whether Peerd is blocked upstream or owes its own implementation.
  4. Remove the entry only after the packaged exit check passes and the weaker fallback/guard is deleted.