We currently rewrite synced tag queries to point to the local tag folder (https://searchfox.org/mozilla-central/rev/152c0296f8a10f81185ee88dfb4114ec3882b4c6/toolkit/components/places/PlacesSyncUtils.jsm#883-905), but not other queries with a `folder=` param. Doing this correctly is tricky. We'd need to parse all outgoing query URLs, include their GUID in the bookmark record, rewrite the query on the destination, and handle the case where we might see an incoming query before we see the folder. This is a similar problem to orphans: queries, like parents, are pointers to other parts of the tree that we might not have yet. In practice, a simpler solution is not to sync `place:` queries at all: * The most common "folder=" bookmarks are the left pane queries, which we a) shouldn't sync at all, and b) use symbolic names like "BOOKMARKS_MENU" and "UNFILED_BOOKMARKS" instead of IDs. * I don't think iOS or Android support them, since they don't use Places! * There's no UI to create these queries, the Web Extension bookmark APIs don't support them, and add-ons that might create them won't be supported in 57.

Standard8 is migrating `folder=<id>` queries to `parent=<GUID>` in bug 824502. \o/