It is easier to download, install popular browsers and test the website. One compelling reason to do so is, browsers keep on sending updates every now and then. If you are using any feature that is not yet widely implemented in browsers, then you can check the same at caniuse.com, for different browser version compatibility.
If you are talking about mobile browsers, it is a different issue. Then lot of other things come into play like device size, orientation, resolution, ppi (or dpi) and default scaling factor. Definitely it is not easy to test website on mobile browsers. Better not use any feature that you doubt all mobile browsers may not support. Always use features that are surely responsive.