Thank you, Jim. That makes two votes for mah-ree, so that's helpful. I thought perhaps it would have a long i sound, but no.

The DT says it was originally written in Gaelic. It would be interesting to hear it sung in Gaelic, then in English, to see if the song differs any depending on the language. Stresses and subtle changes in timing and so forth...

I found the tune on a site from Germany. The melody seemed to be played by a brass band! It was charming, actually.