This seemed like the perfect extension for cataloging offline web pages until...

After saving around 100 pages, every attempted save thereafter results in: "Error: The snapshot has been made, but it could not be stored in this extension's storage. Just saving it among your downloads instead.."

Apparently this extension doesn't invoke Mozilla's "unlimitedStorage" permission and therefore only 2GB of snapshots can be made. After that limit, snapshots are saved in the system's default downloads directory, but cannot be searched via the extension. What a buzzkill.