I'm still running my macs on 10.7 and 10.8, what error message does multibit report under 10.10 ?
OSX hasn't installed java for a few years now, have you tried downloading the latest JRE ?
I get the error message that I need Java 6.
I tried with Java 8 and now I have Java 7 installed, but none work.
I am running OSX 10.8.5, and up until yesterday was running JRE 1.6
I have both Multibit 0.5.18 and MultibitHD PB4
Yesterday I upgraded to JDK 1.8
$ mvn -version
Apache Maven 3.0.4 (r1232337; 2012-01-17 19:44:56+1100)
Maven home: /usr/share/maven
Java version: 1.8.0_25, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/jre
Default locale: en_AU, platform encoding: UTF-8
OS name: "mac os x", version: "10.8.5", arch: "x86_64", family: "mac"
And Multibit 0.5.18 still works normally
If you upgraded an existing OSX to 10.10, maybe the upgrade broke the installation. Backup your Multibit wallet files, and try reinstalling MB?