Created attachment 823468 [details] screenshot I've found a couple of ways to reproduce this: STR #1: 1) Go to about:home and pin any site in positions 2-6 2) Click the thumbnail to go to that site 3) Click back 4) Unpin site If the thumbnails then shift around as a result of the unpin, you'll hit this bug. If the thumbnails don't shift, repeat steps 1-4 until you trigger a frecency change. STR #2: 1) Go to about:home and pin any site 2) Long press any other thumbnail and choose Edit 3) Select the same page that was pinned in step 1 In both STR #1 and #2, the pinned site will have its thumbnail duplicated in another slot. Screenshot attached.
Possibly a dupe of Bug 926430, at least as far as the root cause is concerned.
My fix in Bug 926430 addresses this -- thumbnails are always correct. Duping to that.