I have a ton of duplicates under my Sync account's Devices & Apps
So I use Firefox Sync on 2 devices: my computer & my smartphone. When I am in "Manage Accounts" and look in the "Devices and Apps" section, they are listed a ton of times under several different names (mostly the computer). Interestingly there is a link to the FAQ about missing and duplicate items, suggesting this is a common problem, but the page it links to only addresses missing items. Subsequent searches of the FAQ haven't turned up anything useful either. I've attached a splitscreen image of all the duplicates (with my name and my computer's name blacked out for privacy/security)
Modified