Moonly - js and css injector by Vladyslav Tkachov

Moonly lets you inject custom JavaScript and CSS into any web page. Create scripts, set conditions for when they run, and manage everything through a clean, built-in editor.

What you can do:

• Inject JavaScript or CSS - write either in a full-featured code editor (syntax highlighting, line numbers, bracket matching, and a choice of editor themes)
• Run scripts manually with one click from the toolbar popup, or automatically when a page matches your conditions
• Match pages by exact URL, substring, or regex pattern
• Control injection timing - run JavaScript before the page loads or after (CSS is applied early, with no flash of unstyled content)
• Organize your library - search, duplicate, reorder, and enable/disable scripts
• Import and export scripts as JSON, one at a time or all at once, for backup or sharing

Built for developers, testers, and power users who want to automate repetitive tasks, test page behavior, or customize their browsing experience.

Enabling automatic injection:

Firefox asks for your permission before an extension can run on every site. Manual scripts (run from the toolbar) work right away. To use automatic scripts, open the Script Manager and click "Enable on all sites" to grant access - you can revoke it any time from Firefox's Add-ons settings.

Permissions:

• Tabs - detect the active page for script matching
• Scripting - inject your JavaScript and CSS into pages
• Storage - save your scripts locally on your device
• Access your data for all websites - required to run your scripts on the pages you choose (granted by you, when you enable automatic injection)

Scripts are stored entirely on your device and never sent anywhere. No data is collected. Use responsibly - only run scripts you trust.