Would be nice if librewolf and WaterFox changed their flow to make it clear that Mozilla's Sync Server is being used, and make it opt in with something like: To sync please select one of the options below: [x] Custom Sync Server: ___________ [ ] Mozilla Sync
https://blog.mozilla.org/services/2011/03/22/get-syncing-wit...
Not only one of the first questions would be whether you want to use a Custom Sync Server, but this "Custom Sync Server" could be something as trivial as WebDAV server (if you have any kind of public-facing HTTP server, it almost certainly already supports this, or does so with minimal extra dependencies) . Then it would also ask you for the E2EE key, separately from the login key.