[EDIT]
The last version of MAMP with the last version of OSX Yosemite works fine.

I installed the beta of Yosemite two month ago, no problem with MAMP.
With the last release of OSX, Apache and MySQL did not work.

I found a solution for Apache by using the default port 80 and renaming the file envvars to \_envvars in Applications/MAMP/Library/bin but have not been able to solve the problem with MySQL.