Firefox add-on with keyword - override

New Tab Override allows you to set the page that shows whenever you open a new tab.

Add your own custom CSS styles to any webpage

An extension to help you gain full control of any website by redirecting traffic, replacing, editing, or inserting new content.

Manually set the charset (character encoding) for a webpage, to fix encoding errors and garbage characters on websites. A replacement for the former View -> Text Encoding menu.

I'm sure most of us like halloween, if you don't that's fine; I'd like to give this to those who want something simple to appreciate such a good holiday. :)

Allow to override any content type containing json to application/json. Can be very useful to override vendor specific content type.

Finally, an efficient wide-spectrum content blocker. Easy on CPU and memory.

Gives the ability to set custom user agent string

Firefox on Linux hardcodes tab selection shortcut to alt+1, alt+2 etc. This extension overrides that with ctrl - ctrl+1, ctrl+2 etc.

Quickly translate selected or typed text on web pages. Supports Google Translate and DeepL API.

Allows to add rules to force specific cookie values whenever a website is visited

Easily override the browser's User-Agent string

This extension overrides the default 'Accept' header to prevent websites from serving lossy WebP images instead of the original PNG/JPG

Replace your new tab page with awesome productivity widgets Take Notes, Todos, Google Calendar, Weather...etc.

Simple browser extension for copying links without trackers. Currently supported websites: - facebook.com - messenger.com - instagram.com - google.com - youtube.com

Re-enable the possibility to use the context menu on sites that overrides it

Re-enables the Gopher protocol in Firefox 56 and above, allowing you to enter Gopher URLs and click on Gopher links. Because WebExtensions does not yet have a TCP sockets API, this version redirects your requests to the Floodgap Public Gopher Proxy.

Re-sets the 'Ask to save logins and passwords for websites' to enabled, after the Roboform disabled it. Helpful if you want to have both managers.

An improved refreshed version by TheDoggybrad, originally created by Thomas Wisniewski to override user-agent for Chrome-like Google Search experience.

Override all fonts on web pages with the OpenDyslexic font.

pair of blue tits perched on a cotoneaster bush, Winter, red berries, birds child friendly persona Personas by LisaAtTheBeach

Enable Text Selection on All Websites – Allows unrestricted text selection and copying on any site by overriding restrictive CSS properties.

Overrides the browser's newtab-page with a custom startpage.

Temporarily override blocking for specific needs.

The most popular and feature rich CORS tool on Chrome (over 100K weekly active users) is rebuilt for Firefox with more features. This plugin allows you to send cross-domain requests. You can also override Request Origin and CORS headers.