I would like to know what is the latest version of Firefox Portable for Mac. I just found versions from 2011-2013 and they seem pretty old. By the way, these softwares are not from the official developer (Mozilla).
Like you said there are no up-to-date Portable Firefox for OSX at the moment.
In order to have this to work, it would require to modify the source code to modifiy the directory where Firefox store it's tmp/config files.
I do not know what Firefox Portable for Mac is, but I am running a current version of Firefox on my Macs, you can get it from here: https://www.mozilla.org/en-US/firefox/new/?utm_source=google&utm_medium=paidsearch&utm_campaign=sem2015Q2&utm_term=fast+web+browser&utm_content=speed1
Firefox discusses portable here https://support.mozilla.org/en-US/questions/973932