test: containerized Firefox end-to-end harness (closes #184)

Drives the real popup in a real Firefox with dist/firefox/ installed as an
unpacked MV2 temporary add-on, via geckodriver. Covers popup load, wallet
creation through the UI, and the Add Token screen. Outside make check, like
the Chrome suite.

Zero npm dependencies: tests/e2e/firefox/driver.js is a WebDriver client
over global fetch and child_process against geckodriver's HTTP API. The
Dockerfile pins the node base image, the Firefox 153.0.3 tarball and
geckodriver 0.36.0 by digest.

Errors are read from the privileged nsIConsoleService in Marionette's chrome
context, filtered to non-warning entries whose sourceName is the extension
origin. BiDi log.entryAdded delivers nothing at all for extension pages, so
a Playwright-BiDi or Puppeteer-BiDi harness would see nothing and report
success; the code says so where someone would be tempted to simplify it.
Errors logged during add-on install and background startup are drained and
folded into step 1, never discarded: a throw at the top of
src/background/index.js kills the background page and fails the run.
Content-script capture is left as unverified, because --network none leaves
no http:// page for a content script to be injected into.

Each drain reads the console and clears it in ONE chrome script. Splitting
the read from Services.console.reset() left a window between the two round
trips in which an error was logged into a buffer about to be discarded, and
destroyed unread rather than deferred to the next drain; a probe of 100
sequenced throws at 20ms spacing lost one. With the drain atomic the same
probe accounts for every throw that falls inside the observed window, on two
consecutive runs.

No driver layer is shared with the Chrome suite and the three UI steps are
written twice deliberately: the two backends have no common substrate, and
three steps do not pay for a shim.

Two limits are documented rather than papered over, with measurements rather
than absolutes. Error capture is poll-based, so an error is attributed to a
step and not to a moment within it; the drained window ends ~1.5s after the
last step returns (a 500ms settle, a 1000ms sleep and two drain round trips),
and that cut-off jitters run to run — three runs of throws at fixed offsets
reported everything up to +1.5s and one of the three also reported +1.6s.
Inside the window the atomic drain leaves no race, but nsIConsoleService
keeps a ring buffer of only 250 messages, so more than 250 console messages
between two drains evicts unread errors: 400 throws inside one step report
as exactly the newest 250, on three runs, while occupancy in a clean run
peaks at 4 of 250 at the install drain and 0 at every later drain. Nothing is
stubbed; the container runs with --network none instead, which proves no
request escaped, cannot report which were attempted, and runs only the
failure branches of network-dependent code.

TODO.md

@@ -30,9 +30,10 @@ compiled off.
 
 The backlog lives on the
 [Gitea tracker](https://git.eeqj.de/sneak/AutistMask/issues), which is
-authoritative; this file does not duplicate it. Full policy file set present. A
-real-browser end-to-end suite (`make test-e2e`) now sits alongside `make check`,
-which cannot see a runtime `ReferenceError` in a popup view.
+authoritative; this file does not duplicate it. Full policy file set present.
+Real-browser end-to-end suites (`make test-e2e` for Chrome,
+`make test-e2e-firefox` for Firefox) now sit alongside `make check`, which
+cannot see a runtime `ReferenceError` in a popup view.
 
 # Next Step
 
@@ -44,6 +45,24 @@ undefined identifiers, which is how
 
 # Completed Steps
 
+- 2026-08-12: A containerized Firefox end-to-end harness
+  (`make test-e2e-firefox`) drives the real popup in a real Firefox with the MV2
+  build installed as a temporary add-on. Zero npm dependencies — a WebDriver
+  client over `fetch` against geckodriver — with `node`, Firefox 153.0.3 and
+  geckodriver 0.36.0 all pinned by digest. Uncaught errors are read from the
+  privileged console service in Marionette's chrome context, because BiDi
+  `log.entryAdded` reports nothing at all for extension pages; each drain reads
+  and clears the console in one chrome round trip, so no error is destroyed
+  unread by the drain itself, and errors logged during add-on install and
+  background startup are folded into step 1 instead of being cleared. The two
+  measured limits are documented rather than claimed away: the console ring
+  buffer holds 250 messages (a clean run peaks at 4), and the drained window
+  ends ≈1.5s after the last step returns. Demonstrated discriminating by exiting
+  1 on a `throw` at the top of `src/background/index.js`, on a build with one
+  import removed, on a `setTimeout` throw whose UI assertions all pass, on an
+  unhandled `Promise.reject` and on an undefined identifier in `home.js`, and 0
+  on the branch as it stands
+  ([#184](https://git.eeqj.de/sneak/AutistMask/issues/184)).
 - 2026-08-12: Closed the empty-array hole in the end-to-end unstubbed-request
   guard. `batch.every()` is vacuously true on `[]`, so a POST with body `[]` was
   answered `200 []` instead of failing the suite; the guard now rejects an empty
@@ -252,9 +271,9 @@ tracker.
 - Pre-1.0 security review of the extension (key handling, DEBUG mode policy, RPC
   input validation) before any 1.0rc tag. Individual filed issues are parts of
   it, but the review is broader than any of them.
-- Decide whether docker-in-docker makes `make test-e2e` runnable in the Gitea
-  workflow. Extending the suite itself is tracked as
-  [#183](https://git.eeqj.de/sneak/AutistMask/issues/183) and
-  [#184](https://git.eeqj.de/sneak/AutistMask/issues/184).
+- Decide whether docker-in-docker makes `make test-e2e` and
+  `make test-e2e-firefox` runnable in the Gitea workflow. Extending the Chrome
+  suite itself is tracked as
+  [#183](https://git.eeqj.de/sneak/AutistMask/issues/183).
 - Cut 1.0.0 once the milestone is empty, then continue tagging as milestones
   land.