Consider the following data. The keypath for the objectStore is "id", and the keyPath for the index is "name". { id: 1, name: "a" } { id: 2, name: "b" } { id: 3, name: "b" } { id: 4, name: "b" } { id: 5, name: "d" } { id: 6, name: "c" } When creating a cursor on the index, you should get the following results for the following directions of the cursor: NEXT: key: "a", primaryKey "1" key: "b", primaryKey "2" key: "b", primaryKey "3" key: "b", primaryKey "4" key: "c", primaryKey "6" key: "d", primaryKey "5" NEXT_NO_DUPLICATE: key: "a", primaryKey "1" key: "b", primaryKey "2" key: "c", primaryKey "6" key: "d", primaryKey "5" PREV: key: "d", primaryKey "5" key: "c", primaryKey "6" key: "b", primaryKey "4" key: "b", primaryKey "3" key: "b", primaryKey "2" key: "a", primaryKey "1" PREV_NO_DUPLICATE: key: "d", primaryKey "5" key: "c", primaryKey "6" key: "b", primaryKey "2" key: "a", primaryKey "1" I think currently we get the PREV order wrong. But the PREV_NO_DUPLICATE query seems to execute in a very suboptimal way that doesn't use indexes properly. I *think* I have ideas for how to write SQL queries that produce this result, feel free to ping me.

Comment on attachment 572748 [details] [diff] [review] Patch to fix Review of attachment 572748 [details] [diff] [review]: ----------------------------------------------------------------- Looks great!

Checked in https://hg.mozilla.org/mozilla-central/rev/504d3127b9a6 Thanks again for such a quick review!