Content Quality: Well-structured News piece (465 words, within the 400-1200 range) organized by audience: web developers, security/automation, users/admins, experimental features, unknowns. Almost every bullet maps to a specific line of the MDN or Firefox release notes. Minor issue: the Overview calls the release 'mostly a web-platform conformance and polish update', a mild editorial characterization not found in any source.
Source Verification: Read all three snapshots from disk (gunzip, HTML to text). manifest suspicious_patterns is null for all three; no injection text found. source-0.html.gz (developer.mozilla.org Firefox 156 notes, 200): confirmed verbatim/near-verbatim release date Sept 15 2026; Scheduler.yield() inherits enclosing task's priority and abort signal across an await that settles synchronously; text-box-trim/text-box-edge trim correctly incl. ::first-line font metrics, and 'text-box-trim still has no effect in combination with line-clamp' (the source names only text-box-trim, article extends this to both properties: minor); Promise.try() resolves like Promise.resolve(); using declarations cannot be reassigned; ffdhe2048/ffdhe3072 no longer offered by default; deriveBits() TypeError for NaN, Infinity, negative or > 2^32-1; alwaysNegotiateDataChannels defaults to false; Range.deleteContents()/extractContents() operate on DOM tree; Marionette WebDriver:GetElementTagName returns qualified name, non-backward-compatible for SVG; three experimental features (scoped custom element registries, named-feature(), Container Timing) disabled by default via about:config, scoped registries enabled in Nightly. source-1.html.gz (firefox.com release notes, 200): confirmed release date, macOS open-at-startup, Windows ARM64 hardware H264 WebRTC decoding, and the PDF viewer line. The exact source text is 'Firefox's built-in PDF viewer starts up to 45% faster.' The 45% figure is stated by Mozilla, not derived by the bot, but the qualifier 'up to' is dropped: headline says '45% Faster', summary says 'roughly 45%', body says 'increased by approximately 45%' and 'the approximate 45% figure'. The source also says Windows ARM64 'may now use' hardware H264 decoding; the article says 'now support', dropping the hedge (minor). source-1 also carries the ::first-line text-box-trim line under Web Platform. source-2.html.gz (firefox-admin-docs.mozilla.org, 200): confirmed SitePolicies DisableServiceWorkers ('Firefox 156 only'), Firefox ESR 153 is the current ESR, release date 15 September 2026. Not mentioned in the article but present: FirefoxHome Widgets option and DisableLaunchOnLogin macOS change; the article's 'new enterprise policies' summary phrasing is supported. All three domains returned HTTP 200 without archive fallback. Allowlist: developer.mozilla.org, firefox.com and firefox-admin-docs.mozilla.org are NOT in config/source_allowlist.txt (only blog.mozilla.org is), which is what triggered the automated warning; all three are Mozilla's own first-party primary documentation for its own release, so this is treated as an allowlist gap rather than a reputability problem.
Factual Accuracy: All feature claims trace to the snapshots. One inaccuracy, in the headline, summary and body: Mozilla says the PDF viewer 'starts up to 45% faster' (an upper bound); the article presents 45% as a typical or approximate figure. The lead claim (Firefox 156 released Sept 15 with these features) is fully supported. No fabricated specifics, no invented quotes. The Context section's cross-reference /article/2026-08/07-chrome-edge-and-firefox-converge-on-two-week-release-cycles-in-august-and-september resolves to a published article on disk with the correct singular /article/ form, and that article does say Firefox moves to a two-week cadence; the clause 'browser vendors move to shorter release cycles' is supported by that prior article, not by the three cited sources, which is acceptable for an internal link.
Overall Assessment: Substantively accurate, well-sourced release-notes coverage. The only real defect is the loss of the 'up to' qualifier on a headline number, which a single corrections note honestly covers, so APPROVE_WITH_CORRECTIONS.