zoom keeps returning to default settings

everything on the web is too small. I have to hit cmd + on every page to zoom it to a size big enough to read. I am ok with this.

The problem is that halfway through reading the page, the computer will suddenly, for no apparent reason, switch back to the default size. Why does it do this. It is highly annoying.

OSx 10.9.3

Tell us which browser you're using? If it's Safari, I can show you a way to keep the zoom up and enlarged.