Your logic on this matter escapes me.
You are not very tech/Mac saavy.
The new OS X Yosemite is a completely new operating system that bears little resemblance to the OS X 10.6.8 Snow Leopard that you are using, now.
You think FireFox is more complicated for you to use than Safari, so, instead of just changing/switching web browsers and learning to use it and know it like you know your older Safari version, you rather spend your time backing up your current system (which you should be doing regularly, anyways), download and install a brand new OS X Yosemite and having to relearn a completely new and more complicated OS X upgrade AND, also, have to relearn the newer Safari browser version.
Does this approach really make more sense to you???
Your choice.
Do what you will, but installing and learning a new web browser seems A LOT easier to me than having to relearn an entire OS and newer Safari.
To each their own.
Good Luck with whatever you decide