Small pieces of code your browser runs on a website you don't control, so it behaves the way it should have in the first place. Three things to do, in order.
A userscript is a text file your browser loads on the sites named inside it. It can restyle a page, add a panel, or fill in a field: anything you could do by hand, done for you.
One extension, set up once: Tampermonkey. About two minutes, and then you never touch it again. The steps are below, with pictures.
A userscript runs with full access to the pages it matches, which is exactly why it can fix them. Only run ones you, or someone you trust, have read. Every script here is plain commented source you can open before installing.
No network requests, no analytics, nothing leaves your browser. Settings stay on your machine, and every feature has an off switch.
Not allowed to install extensions? Skip to running them from a bookmark at the bottom of this page.
Once, in this order. The pictures are Microsoft Edge; Chrome looks all but identical. On Firefox, only the first step applies.
Get it from tampermonkey.net or your browser's add-on store, and let the install finish.
Install one manager: two will run the same script twice. Prefer a different one?
Right-click the Tampermonkey icon in the toolbar and choose Manage extension. While that menu is open, set Site Access to Allowed on all sites.
On the page that opens, turn Allow User Scripts on. Check that Site access reads On all sites while you are there.
Chrome and Edge split this in two on purpose: the permission on its own shows no warning at install time, so the toggle makes running userscripts a decision you took knowingly. If your browser is old enough not to show the toggle, switch on Developer mode at the bottom of the extensions page instead. Firefox needs neither.
Press Install userscript on any script in the catalogue. Tampermonkey opens its install screen with the full source, so you can read it, confirm, then visit the site. Updates arrive on their own after that.
Everything here is a standard .user.js file, so any of these
will run it.
| Manager | Browsers | Licence | Notes |
|---|---|---|---|
| Tampermonkey | Chrome, Edge, Firefox, Safari, Opera | Free, closed source | The default: most used, best tested, cloud sync. |
| Violentmonkey | Chrome, Edge, Firefox, Opera, Firefox Android | MIT, open source | Auditable, asks for fewer permissions. Same scripts. |
| Greasemonkey | Firefox | MIT, open source | The 2005 original. Dropped some old APIs, so older scripts can fail. |
| FireMonkey | Firefox | MPL-2.0, open source | Scripts and styles in one extension. Small user base. |
The library lives on its own page, where you can search it and filter by site. Each entry lists what it does, how it works and where it falls short, with the full source one click away.
Optional: nothing below needs an extension
If extensions are blocked on your machine, or you only want a tweak for five minutes, these work without installing anything.
Rolling this out to a team? IT can push a manager and a script list
through managed browser policy (ExtensionInstallForcelist plus the
extension's managed storage), so nobody has to do the setup steps at all.