Firefox Places schema migration vs. profile downgrade: rollback safety guarantees

Direct answer

No. Firefox Places does not expose an internal API or flag to verify schema integrity before a downgrade, and there is no supported way to force user_version to a lower number without risking a profile reset. The migration framework is forward-only.

Confirmed facts

• Places schema changes run as individual SQLite transactions on startup and update PRAGMA user_version.
• SQLite WAL or journal atomicity protects each migration step from a partial write, but it does not preserve the previous schema or allow cross-version downgrade.
• Generic checks such as PRAGMA quick_check and PRAGMA integrity_check confirm file consistency only; they do not confirm compatibility with an older Firefox build.
• Setting PRAGMA user_version to a lower value does not reverse added tables, columns, indexes, or triggers. On a live profile it can produce missing-column errors, assertion failures, database damage, or a profile reset.

Likely behavior and uncertainty

An older Firefox binary opened against a migrated Places database may ignore bookmarks and history, refuse to use Places, or recreate the database. Whether it resets the profile depends on the exact target build and version distance, so treat this as likely rather than guaranteed. Exact user_version values and migration step lists differ by Firefox release and ESR.

Steps for this case

1. Close Firefox completely so the WAL sidecar files are checkpointed.
2. Back up the profile folder, or at minimum places.sqlite, places.sqlite-wal, and places.sqlite-shm, to a test location.
3. Open the copied database with SQLite and run PRAGMA user_version;. Record the value.
4. Run PRAGMA quick_check; and PRAGMA integrity_check; on the copy as a consistency check, not a compatibility guarantee.
5. Launch the target Firefox build against the copied profile in a separate profile directory and confirm bookmarks, history, and Places functions before touching the primary profile.
6. If user_version is higher than the target build expects, do not force it lower. Export bookmarks from the current Firefox or remain on a compatible version.

Missing diagnostic detail

Provide the exact target Firefox build/version and the current PRAGMA user_version from the copied database. That detail changes the recommendation because compatibility is version-specific.