Bookmarklets are basically little pieces of javascript, stored as a bookmarked URL that can be used on a page. Drag the link in the left column to your bookmarks toolbar (Chrome: Ctrl+Shift+B to toogle toolbar; Firefox: View | Toolbar | Bookmarks Toolbar) to add to your toolbar for quick access. I keep them under a bookmarklet folder there.

Bookmarklet Note
Easy Read The one I constantly use. When you come across a page you can’t read because of some nasty colour clashes click on this and the page will be stripped of it’s colour.
Google translate Translates open page to English.
WatchThatPage Adds the current page to your list in watchthatpage, you will have to select if it’s to be monitored daily or weekly
Creating a CSV From an HTML Table Example to export a confluence html table to csv. Source:
PrintLiminator PrintLiminator allows you to remove page elements and applying different styling for printing.
PageZipper PageZipper appends additional article pages underneath first page.

More info on bookmarlets and the more advanced user scripts: