Mac install procedure:
1) Click on download link (downloads a .dmg that automatically mounts (after you authorize) and opens the mount in the Finder)
2) Drag the Firefox app to the "Applications" folder ("Replace the older version?" Sure! WTF!)
3) Ta Da! Congratulate yourself! Yet another complicated Mac install behind you! Well Done!!!
Then again, you needn't follow step 2 exactly. Copy it anywhere you darn well please, just 'cus you can.
'Cus it's a Mac....
So there.....