fix: AutistMask does not run in Firefox private windows (closes #646)

Firefox gives an extension page in a private window locks of its own. A
popup there could save between the background's read and its write of the
stored record, and undo a network switch the background had saved.

manifest/firefox.json now sets "incognito": "not_allowed", so Firefox never
runs AutistMask in a private window. tests/manifest.test.js pins the key.
The README and five code comments no longer describe a private-window
exception to the lock.

Model: opus-5-5

README.md

@@ -1494,16 +1494,16 @@ wrote last, the record says which build's shape it is in.
 Each write reads the record, changes it and writes it back, holding a lock from
 the read to the write: the browser's own (`navigator.locks`), taken through
 `withLock()` in `src/shared/browserApi.js`. Every page of the extension and its
-background share it. Firefox gives a page in a private window locks of its own.
+background share it. `manifest/firefox.json` sets `"incognito": "not_allowed"`,
-`manifest/firefox.json` sets `"incognito": "not_allowed"`, so such a page cannot
+so no page runs in a Firefox private window. Firefox would give a page there
-read or write extension storage. In Chrome, a page opened from an incognito
+locks of its own. In Chrome, a page opened from an incognito window still runs
-window still runs outside incognito and shares the lock. The popup's
+outside incognito and shares the lock. The popup's `saveState()`, the
-`saveState()`, the background's `updateState()` and the StateRecovery reset all
+background's `updateState()` and the StateRecovery reset all take it, so no
-take it, so no write lands between another write's read and its write, where it
+write lands between another write's read and its write, where it would be lost.
-would be lost. Chrome has it from version 69, older than any Chrome that runs a
+Chrome has it from version 69, older than any Chrome that runs a Manifest V3
-Manifest V3 extension, in pages and in the service worker; Firefox from version
+extension, in pages and in the service worker; Firefox from version 96, older
-96, older than the 115 `manifest/firefox.json` declares. Where it is missing, a
+than the 115 `manifest/firefox.json` declares. Where it is missing, a write
-write fails rather than going ahead without it.
+fails rather than going ahead without it.
 
 Version 1 is the shape that shipped before versions existed, so a stored record
 with no `schemaVersion` is version 1 rather than a defect: it loads normally and

docs/README.md

@@ -208,8 +208,6 @@ password.
 3. Click "Load Temporary Add-on".
 4. Select `dist/firefox/manifest.json`.
 
-AutistMask does not work in Firefox private windows.
-
 ## Getting Started
 
 ### Creating a New Wallet

tests/manifest.test.js

@@ -169,7 +169,7 @@ describe("declared icons", () => {
 // save could land between the background's read and its write (README,
 // "Stored state and its version").
 describe("private windows", () => {
-    test("a page in a firefox private window cannot read or write extension storage", () => {
+    test("firefox never runs AutistMask in a private window", () => {
         expect(readManifest("firefox").incognito).toBe("not_allowed");
     });
 });