Tampermonkey is a free browser extension and the most popular userscript manager. It's available for Chrome, Microsoft Edge, Safari, Opera Next, and Firefox. Even though some of the supported browsers have native userscript support, Tampermonkey will give you much more convenience in managing your userscripts. It provides features like easy script installation, automatic update checks, a simple overview what scripts are running at a tab, a built-in editor and there is a good chance that incompatible scripts run fine with Tampermonkey. So give it a try!