Hi sirshootalot, you don't give a lot of information but first place to start would be to hit the CTRL+0 keys - that's CTRL and zero key together. Just in case you have altered the size by mistake. Or you could try the opposite and, while holding down CTRL, use your mouse wheel to increase the size in search.
You don't say if it has changed on other sites.
See. Popper, knows what he's talking about 😄 Just to add you need the View/Zoom menu on Firefox menu bar 🙂