A minimalistic Firefox extension that allows you to define one JS script which is injected into every page you visit. The addon's code is only a couple of lines long so you can easily verify what's going on.

run-a-script promo image
What is run-a-script?

"run-a-script" is a minimalistic Firefox extension that enables you to inject a JS script into every web page you visit. It provides security and the ability to review the code.

Stats date:
Users: 63 ▲ 2
Rating: 5.00 (2)
Version: 1.0.2 (Last updated: 2023-11-25)
Creation date: 2022-03-22
Weekly download count: 8
Firefox on Android: No
Manifest version: 2
  • storage
  • <all_urls>
Size: 63.68K
Risk impact: Moderate risk impact
Risk likelihood: Moderate risk likelihood

Other platforms

Not available on Chrome
Not available on Edge

A Firefox extension that allows you to define exactly one JS script and inject it into every web page you visit. It uses Firefox' userScripts feature which sandboxes JS code before execution. You should be safe from even the most malicious of actors out there. For at least some convenience, jQuery is injected as well and usable from your script. The code of the extension is deliberately minimal, you are encouraged to review it for security before running the extension.

run-a-script is meant for people with trust issues. There are plenty of extensions out there that you could easily re-implement with a small JS snippet instead of installing. Also useful with uBlock Origin for defeating aggressive sites.

The plugin supports:

  • sandboxed injection of 1 script + jQuery into all pages, you need to refresh the opened ones
  • enabling / disabling the script
The plugin does NOT support:
  • Android – but working on it
  • Chrome – the whole idea of this extension is to be secure but that's irrelevant if your browser is a black box
  • saving to and loading from a file – saving would be useful but currently not possible due to a Firefox bug
See the homepage for a usage example.
Risk impact

run-a-script may not be safe to use and it requires some risky permissions. Exercise caution when installing this add-on. Review carefully before installing.

Risk likelihood

run-a-script is probably trust-worthy. Prefer other publishers if available. Exercise caution when installing this add-on.

Upgrade to see risk analysis details