Installed extensions "Multiple tab handler" on a clean install of Waterfox 44 (believed to be identical behaviour to firefox 44 for this sort of thing) with no previous profile.
Opened 5 tabs to random URLs (google, microsoft etc).
Selected tabs 3 and 5, and dragged them to between tab 3 and 4.
Expected result:
12345 -> 12354
Actual result:
12345 -> 12534
(the dragged tabs were dropped/inserted in reverse order)
Expected result: 12345 -> 12354
Actual result: 12345 -> 12534 (the dragged tabs were dropped/inserted in reverse order)