Random collection of userscripts
If you don't know what a user script is, it is a script that lets you customize how the way a webpage displays things on your end. If you are familar with browser-addons, a userscript is similar to that except it is more limited in what it can do and it is generally easier to view the source code of userscripts. In fact, an add-on is actually required just to be able to run userscripts.
The two most popular are:
- Violent Monkey (open-source)
- Tampermonkey (not open-source)
You may also see references to Greasemonkey, which is the addon that first made userscripts possible. Greasemonkey is not as well supported these days and has fallen behind the other 2. Since Tampermonkey and Violent Monkey are both based on Greasemonkey, most userscripts will work fine in either one.
Both add-ons can be run on most Chrome- or Firefox-based desktop browsers including: Firefox, Waterfox, Pale Moon, Google Chrome, Chromium, Brave, Opera, Vivaldi, and Edge. Possibly others.
On Android, I can confirm that the Kiwi browser supports Chrome add-ons. As of the time of writing, Firefox mobile only supports a very limited set of very specific add-ons and I don't think the two addons above are supported (Going off an article I read a few weeks ago; I did not confirm this myself).
Most of my userscripts are in Violent Monkey using Firefox or Waterfox.