KH4 Companion is live on addons.mozilla.org. It is the first thing I have ever shipped to Mozilla, and it went out as version 0.2.0 — the same build that has been on the Chrome Web Store since 19 August, not a fork and not a stripped-down cousin.
What the port actually took
Less than I expected. It was mostly manifest work: an add-on id under browser_specific_settings.gecko, a background entry that keeps the MV3 service_worker key for Chrome and adds a scripts fallback for Firefox, and the data collection declaration Mozilla now asks every submission to make. That last one is the easiest form to fill out when the honest answer is none: no analytics, no account, no telemetry, nothing leaving the machine.
The extension itself did not change. Same countdown to the announced Late 2027 window, same days-left toolbar badge, same milestone tracker, same news and trailer feeds, same original-prose lore compendium, same three-lane Keyblade Strike minigame. The code was already written the way that makes this cheap — pure logic modules with no DOM and no clock of their own, and a service worker that relays rather than remembers — so there was nothing browser-specific hiding in the parts that matter.
Where to get it
Firefox: KH4 Companion on addons.mozilla.org. Chrome: KH4 Companion on the Chrome Web Store. Both are free, both collect nothing, and the full feature list and privacy policy live on the KH4 Companion project page. The build story is in the earlier devlog, Counting down to a date that does not exist.
KH4 Companion is an unofficial fan project. It is not affiliated with, endorsed by, or connected to Square Enix or Disney, and it uses no game assets, no logos and no copyrighted text.