On pages which do not have a Table of Contents, but should do, create one! (I actually use this as a bookmarklet, so I can load it onto the current page only when I want it.)

Adds a "visited" colour to pouet.net, so you can see which pages you have already visited.

Read articles hands-free! Pres Ctrl-Down or Opt-Down to start slowly scrolling the page. Press again to adjust speed. Escape or Space to stop.

Intercepts console.log calls to display log messages in a div floating on the page. Tries to be a replacement for normal browser Error Consoles (which can be a little slow to open).

Add History box at wikimedia's leftmost column

If a tab is unused for a long time, it switches to a light holding page until the tab is focused again. This helps the browser to recover memory, and can speed up the re-opening of large sessions.

Shows Delicious info for the target page in a tooltip when you hover over a link.

Adds a favicon for the website next to every external link on the page. Clearly shows when you will be leaving the current site, and where you will be going! (Unfortunately making links longer than expected can result in unwanted overflow on various websites. For example, Google header bar!)

Quick scroll to next/previous image on a page with n/p buttons

Extends DDG by adding a customizable list of additional search engines for making fast searches from other engines.

Adds the likes/dislikes light-saber to YouTube thumbnails, so you can avoid watching crap videos. Activates when mouse passes over a thumbnail.

Adds some extra keystrokes to Firefox.

Make the guardian great again!

Makes READMEs on npmjs.com look more like READMEs on GitHub (font, size, padding, some colors); also makes the content wider

The red notifications dots on Quora are annoying, so let's make them grey. Also hide the popups, separate adverts from content, don't keep opening new tabs, and add some whitespace for readability.

Load more results automatically and endlessly.

Four visual improvements for Wikipedia (and other wikis): Indents sub-sections to make the layout clearer. Hides the sidebar (toggle by clicking the header). Floats the Table of Contents for access when scrolled. Converts heading underlines to overlines.

Navigate sideways! When you click a link, related links on the current page are carried with you. They can be accessed from a pager on the target page, so you won't have to go back in your browser.

Adds favicons next to Google search results. Also works for Ecosia, StartPage and Searx.

Sort user's Github repositories by popularity (only applies to those visible on the current page)

When clicking the notifications icon, displays notifications in a dropdown pane, without leaving the current page.

Tampermonkey keeps asking us to select an account when we open the browser. But this script by Jack'lul will do it for us!