How do I permanently set the zoom-function, so I will not have to zoom every time I open a new tab/page?

I have recently installed Firefox on my one month old laptop which has a 17" screen. Every time I open Firefox I have to use the zoom-function (ctr +) four times to be able to read comfortably. Every time when I next open a website, or tab, or window I have to use the zoom-function again. This is kind of getting old, fast. Is there any way I can set the zoom to a higher/closer setting permanently, so I do not have to use the zoom-function about 50 times everytime I use the internet? If you could help me that would be lovely! Thanks, Kikki