Does it derive from Latin mandatum, or perhaps from an Anglo-Norman form of the word maund, woven basket?
We don't have a surviving form of this word in Jèrriais, but our mainland cousins preserve what seem to be forms of the word:
In mainland Norman, there’s a diton:
Givre à Noué
poumes à pllen maundelet
(frost at Christmas, apples by the basketful)
mâone is defined in the Dictionnaire Français-Normand (2013) as a round wicker two-handled basket carried on the back by fisherfolk for carrying fish; also a round basket in which lines are coiled ready for use. The Dictionnaire Normand Français (2012) gives further information and notes that attestations are from the Hague and Val de Saire areas of the Cotentin, and that nowadays mâones are more typically made of plastic or metal.
There’s also the quantity word mâonaée: a basketful of mackerel or other fish in a mâone.
Cherbourg writer Jean Tolvast (1870-1945) published a story “Maônet-Picot” – in which the character is being described as being so small he could fit into a mâone.
The loss of -d- wouldn’t be a surprising development.