Action Lock (Deterministic Execution)

Phase 2 — Freezes the page completely while the AI browser agent is thinking. No JavaScript, no timers, no layout reflows, no animations, no events. The page the agent analyzed is exactly the page it acts on. This is essential for reliable browser automation — without deterministic execution, agents act on stale state.

The Problem

Between reading the page and executing an action, the DOM can change. JavaScript timers fire, CSS animations move elements, network callbacks update content, and event handlers reshape the layout. The agent clicks where a button was, not where it is.

How It Works

Action Lock patches Firefox’s C++ core (nsDocShell) with two new methods:

suspendPage() — freezes the refresh driver, suspends all timers/intervals/network callbacks, and suppresses event handling
resumePage() — reverses the freeze in opposite order

The freeze pipeline:


Page.setActionLock({enabled: true})
        │
        ▼
  1. allowJavascript = false  (all frames)
        │
        ▼
  2. nsRefreshDriver::Freeze()
     - No layout reflow
     - No CSS animation ticks
     - No requestAnimationFrame
        │
        ▼
  3. nsPIDOMWindowInner::Suspend()
     - setTimeout/setInterval paused
     - Promise microtasks held
     - Network callbacks queued
        │
        ▼
  4. PresShell::SuppressEventHandling()
     - Mouse/keyboard events dropped
     - Mutation observers paused

  ═══════════════════════════════
  Page is now deterministically frozen
  ═══════════════════════════════

Page.setActionLock({enabled: false})
        │
        ▼
  Thaw in reverse order: 4 → 3 → 2 → 1

Protocol


// Freeze
{"method": "Page.setActionLock", "params": {"enabled": true}}
 
// Thaw
{"method": "Page.setActionLock", "params": {"enabled": false}}

If the page navigates while the lock is held, the lock is automatically released. This prevents deadlocks from agents that freeze a page and then navigate away.

Configuration

Action Lock is enabled by default (the method is available). To disable the capability entirely:


vulpineos.actionlock.enabled = false

Files Modified

patches/action-lock.patch — C++ patch adding suspendPage()/resumePage() to nsDocShell
additions/juggler/protocol/Protocol.js — Page.setActionLock method definition
additions/juggler/protocol/PageHandler.js — handler routing
additions/juggler/TargetRegistry.js — PageTarget.setActionLock() IPC bridge
additions/juggler/content/main.js — content-process freeze/thaw logic
settings/camoufox.cfg — vulpineos.actionlock.enabled preference