For informational purposes. I recently upgraded to Mavericks 10.9.5 and am running PT HD 10.3.8 on a 2008 Mac Pro 3.1. In search of a compatable browser I discovered Chromium which does really well with most sites I tried it on. After letting Mavericks update itself Safari got better, but still not perfect.
I was also shocked that Antelope Audio's USB driver/launcher for my Zen Studio+ which explicitly stated "Mac OS X 10.12" minimum installed, loaded and worked like a champ, as well as it does on my mid-2015 rMBP running Mojave. I'm starting to like Mavericks and I was scared of it before. I was on Mountain Lion 10.8.5.
Link To Chormium