This is Adam Katz's collection of UserScripts for Greasemonkey (install on Firefox), Violentmonkey (install on Chrome) and similar website modifiers.
To install, first get a userscript add-on for your browser, then view the code for the desired script. Click the Raw button at the top right of the code to engage the add-on for installation. Then load (or reload) a page it affects.
Some of these are old enough to have previously existed at the now-defunct userscripts.org. See also this 2014 archive of my userscripts.org scripts.