Auto-advance dropped the next chapter if the browser evicted the service worker mid-navigation. The pending tab, its content type and its next-chapter URL lived in module-level Maps, which an MV3 worker loses the moment it is evicted, so tabs.onUpdated woke to an empty set and the new page never started scrolling. All three now live in storage.session.
Resume positions were never saved. They were written to storage.sync, where 50 full URLs overflow the 8KB per-item quota; every write rejected, and the rejection was discarded. They are stored locally now, and a failed write is reported instead of swallowed.
Resume did nothing on reader and app-shell layouts. The position was read from document.scrollingElement and restored with window.scrollTo, but on a page whose document does not scroll that saves and restores a permanent zero. Both ends now use the element the engine actually scrolls.
The floating widget froze in step mode. startStepMode() never emitted state, so the progress ring and the play glyph stopped updating between start and stop.
The Shortcuts page showed the defaults rather than the real bindings. It rendered a cached copy from storage, so a shortcut rebound in the browser's own editor still displayed as Alt+S. It now reads commands.getAll().
Badge writes could take down a message handler on Firefox for Android, which exposes action without badge support. They are guarded.

strict_min_version is now 115.0, the first Firefox with storage.session. Firefox 109 to 114 are no longer supported.

The unused profile:getForSite and profile:save message handlers, and the customShortcuts storage item that nothing wrote to.