Firefox keeps its lock files inside each profile, not at the user-data root, so
the running check never found them and offered imports from a live, mid-write
database. It now walks the source's profiles and looks for all three names the
platforms use.

Firefox isolates cookies per container and per private window through
`originAttributes`. Electron has no equivalent, so importing them all collapsed
several identities onto one host/name/path and handed the profile whichever
container was written last. Only the default container is imported.

The sidecar copy no longer ignores every error alongside the missing-file case;
the new snapshot test caught that the earlier fix had landed on the
pre-extraction copy of this code rather than the shared module.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>