Userscript is a really good tool to tamper with the web.

What can you do with Userscript?

Nearly anything you can accomplish using DevTools can be achieved through userscripts. It would improve your browsing experience.

• Redirect to Old Reddit
• Get YouTube Subtitles: document.querySelector("#movie_player")?.getPlayerResponse()?.captions?.playerCaptionsTracklistRenderer?.captionTracks
• Add websites shortcuts, for example, "jkl", "<>" to videos

Doing console.log in the script will also log in the browser console, so it's easy to debug.

Much Easier Than Extensions

You can write any script and use it right away across browsers. You can use Tampermonkey, Violentmonkey, Greasemonkey, Firemonkey, etc. To begin with, you must have an icon and manifest for every extension. You must also submit 2 very specific pixeled images for the app and specify some other things and justify why you would need this and need that permission. You can't publish MV2 extensions anymore. Userscripts is just like running code like in the dev console.

Developer console is a great tool to use because you can look into every requests to make in the webpage.

Mobile

Chrome on Android doesn't support extensions.

These browsers support extensions:

• Microsoft Edge (Doesn't support most extensions, need workaround in Canary version, support TamperMonkey and a few "approved" ones)
• Safari (Not available on Android)
• Yandex Browser (bans Tampermonkey and Ublock Origin, it works on a whitelist. Ublock Origin dev and ViolentMonkey works)
• Firefox (Firefox removed Ublock Origin Lite from its add-on store)
• Kiwi Browser(Discontinued, some websites may break, for example, YouTube and ChatGPT)
• Mises Browser, Lemur Browser, etc