Muse Breaks is written in the key of F Minor.
According to the Theorytab database, it is the 8th most popular key among Minor keys and the 20th most popular among all keys. Minor keys, along with major keys, are a common choice for popular music. The three most important chords, built off the 1st, 4th and 5th scale degrees are all minor chords (F minor, B♭ minor, and C minor).
See the F Minor Cheat Sheet for popular chords, chord progressions, downloadable midi files and more!