Whenever you make a long or high jump, you can roll a d8 and add the number rolled to the number of feet you cover, even when making a standing jump. This extra distance costs movement as normal.
If you have a multiplier on jump distance, such as that provided by the Boots of Striding and Springing...
In addition, you can jump three times the normal distance, though you can't jump farther than your remaining movement would allow.
... would the +1d8 feet from Mirthful Leaps be multiplied by 3 as well?