Generally speaking, you _can't_ prevent a page from being able to tell what browser you're using. Even with JavaScript completely disabled, there's probably still some quirks with the way different browsers handle CSS or image loading that would give away that information. Even curl can be "fingerprinted" this way, because curl is one of the only "browsers" that doesn't process CSS or images at all.

If you just want to prevent yourself from being identified as an individual, that's a different problem. Tor browser does a pretty good job of solving that.