Re: Mackmyra
No.
Myr is a kind of wetland, the closest word I can think of right now is "bog".
From wikipedia page for Mackmyra (the nearby village): "Namnet Mackmyra är sannolikt bildat av ordet mack (ett slags knott) som brukade dansa över myrarna som omger bruket."
= > "The name Mackmyra is most likely formed by the word mack (a kind of black fly) which used to dance over the bogs surrounding the ironworks"