IMac :: Any Possibility To Increase Font Size On System?

I'm new to IMac and I did a quick search and found nothing. I got an IMac less than 24hrs ago. With the IMac I find that I struggle to read things even with my glasses on. Is there any possible way of changing the system font so I can make it larger? Trying to read things on the imac is actually giving me a headache because my eyes are straining so much.

I'm using FireFox which is great because once you make the page larger (cmd & +) it remembers so when you go back there the page is still large and readable but things like the toolbar is unreadable. Some sites I've been on even with the page zoomed in some of the writing remains tiny and unreadable. I have the 27" IMac and to have the toolbar font so small on such a big screen seems very silly to me because it's unreadable.