Should I throw away a jar of olives that fizzed and bubbled upon opening?
Short answer:
Yes, throw it away.

Long answer:
Bubbling, fizzing, pressure etc. indicates some kind of microbiological activity that is unwanted for properly canned food - canning should eliminate these organisms. Any behaviour like the one you described indicates that something went wrong, so you can not assume the contents of the jar or can to be safe.