Fix gesture drag-drop dying when the <all_urls> permission is missing

[QingJ01]

Problem

After a Firefox update, the gesture drag-and-drop feature (drag a link/image to open it in a new tab, drag text to search) silently stops working — no error, drag just does nothing. Other features keep working, which makes it look like a mysterious partial failure.

Root cause

<all_urls> is an optional permission (manifest.json optional_permissions). The gesture content script is registered from bg/gestureDragDrop.js based only on the gesture.enabled storage flag:

browser.storage.local.get({"gesture.enabled": false}).then(data => registerOrUnregisterScript(data["gesture.enabled"]));

But browser.scripting.registerContentScripts({ matches: ["<all_urls>"], ... }) succeeds even when the host permission isn't granted — it just injects into no page, so drag dies silently. After a browser update that reinstalls the system add-on, the optional <all_urls> grant can be reset while gesture.enabled stays true → the script stays "registered" but inert, and drag is dead with no error in the console.

A second desync in options/options.js: when <all_urls> is revoked it only does checkbox.checked = false, which does not fire the change event, so gesture.enabled is never written back to false and the background never unregisters the inert script.

Fix

• Gate registration on both gesture.enabled and permissions.contains(<all_urls>) via a new isGestureUsable() helper.
• Centralize through syncScriptRegistration(), called on startup, on storage.local.onChanged, and on permissions.onAdded/permissions.onRemoved — so the script always reflects the real (flag ∧ permission) state.
• Make registerOrUnregisterScript idempotent (unregister-then-register) so a registration persisted from a previous session is replaced instead of colliding with "already registered".
• In options.js, write gesture.enabled = false to storage when <all_urls> is revoked, so the flag no longer desyncs from the permission/script state.

Scope / testing

Only extension/bg/gestureDragDrop.js and extension/options/options.js change.

• npm run lint (eslint plugin:mozilla/recommended) passes.
• Verified on Firefox 140 ESR (China build) via web-ext run: drag-and-drop works again after the fix.

🤖 Generated with Claude Code

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