v5.6.0

Firefox reaches full protocol parity: every formerly Chromium-only
feature now works on Gecko, over RDP or the agent bridge.

Added

• extension_list_extensions works on Firefox-family sessions. It rides
  the Remote Debugging Protocol root actor's listAddons over the
  rdpPort the engine stamps into ready.json from extension.js 4.0.15
  on (upstream entry 78). Entries list INSTALLED add-ons regardless of
  live contexts, temporarilyInstalled marks temporary loads, and the
  dev session's extension is flagged ownExtension by matching the
  ready contract's identity (with a lone temporary install as the
  fallback signal). Add-on targets are never attached to or evaluated
  in; system and hidden add-ons are filtered out. Older engines get a
  hint naming the 4.0.15 requirement instead of a generic failure. A
  minimal RDP client (src/lib/rdp.ts) carries the handshake; legacy
  RDP was chosen over WebDriver BiDi on purpose, since BiDi is
  single-session and would block attaching alongside other consumers.
• extension_dom_inspect listTargets works on Firefox: RDP tab
  descriptors as {actor,url,title,type}, with the same two-id-space
  warning as the CDP path (an actor id is not a chrome.tabs id).
  Discovery therefore needs no allowControl on Gecko, unlike listTabs.
• extension_source_inspect closes its four Gecko gaps. dom_snapshot
  and extension_roots ride the bridge eval, embedding the same CDP page
  scripts Chromium uses (the bridge html path also gained the
  shadow-aware serializer, so open extension-root shadow content is in
  the markup now). console rides the RDP watcher's cached-resource
  replay (getWatcher with server target switching, then
  watchResources; verified live that getCachedMessages is a dead end
  on current Firefox), summarized in the same shape as the CDP console
  buffer. deepDom walks CLOSED shadow roots through
  tabs.executeScript, where Firefox exposes
  Element.openOrClosedShadowRoot to content scripts, so it needs an
  MV2 session with host permissions for the target url; a failed walk
  reports why in notes instead of silently dropping the field.
• MV2 page-eval fallback: the engine's page-context eval needs
  chrome.scripting, an MV3-only API, so Firefox MV2 sessions reported
  every bridge inspection as Unsupported. The inspect expression now
  falls back to compiling in the tab's content-script sandbox via
  tabs.executeScript, which reads the identical DOM; callers see the
  same result shape on both paths.

Fixed

• Act-verb CLI output over ~8KB no longer truncates. The engine CLI
  exits without draining stdout, and the socketpair pipe Node hands a
  child buffers about 8KB, so any larger --output json frame (a DOM
  snapshot, a big html capture) arrived cut mid-JSON and surfaced as
  "CliError: extension exited with code 0". The MCP now hands the child
  file descriptors and reads them after exit, which no pipe buffer can
  truncate. Filed upstream as extension.js ledger entry 79; the
  workaround stays until the engine flushes before exiting.

Known limitation

• Firefox MV3 sessions cannot use the bridge extras: the MV3 event page
  CSP blocks the eval the control bridge dispatches through the
  background, exactly like Chromium MV3 service workers. MV2 sessions
  are fully covered via the executeScript fallback. The RDP paths
  (list_extensions, listTargets, console) work on both manifest
  versions.