https://tampermonkey.net/ is a userscript manager for Google Chrome, Microsoft Edge, Safari, Opera Next, and Firefox.

Tampermonkey allows users to apply customized javascript to sites, to alter how the sites look and/or behave. Multiple websites can even be "mashed up" via cross-site scripting techniques. (Tampermonkey scripts have fewer security restrictions than ordinary javascript).

Tampermonkey differs from native Chrome userscripts in that Tampermonkey supports almost all of the Greasemonkey API, and Tampermonkey scripts are now easier to install and manage than native userscripts. Installation is not restricted to Google's store, so popular sites like http://userscripts.org/ still work.

Tagging Guidance:

Please do not tag Tampermonkey questions with userscripts, unless the script is meant to also work as a native Chrome userscript (which is usually not the case).

References and Resources:

• The Tampermonkey page at the Chrome Web Store.
• Tampermonkey FAQ, Documentation and User Guide.
• Tampermonkey Forum.
• Tampermonkey Project (Source/Issues) at GitHub.
• http://userscripts.org/ for many premade scripts. Note that most scripts written for Firefox Greasemonkey will also work with Tampermonkey.
• greasemonkey -- Many of the scripts and techniques, used with Greasemonkey, will work with Tampermonkey. Not all will, but vastly more than those that work with Chrome's native userscripts.
• The tag wiki of userscripts, for an overview of scripting across browsers.