CSS and JavaScript injection

How injection works

Every rule in JustZix is a small piece of code tied to a place on the web. You pick where it applies — a whole domain like example.com or a precise URL path — paste in CSS, JavaScript, or both, and save. From then on the extension injects that code automatically every time a matching page loads. There is no build step and nothing to run by hand.

Each rule has its own editor with syntax highlighting, line numbers, a search bar and a light or dark theme. You can keep dozens of rules side by side and switch any of them on or off with a single click on the floating toolbar.

CSS — instant restyling

CSS is injected through a <style> tag in the document head, so your rules carry full specificity and can override almost anything the site ships. Hide a cookie wall, widen a cramped reading column, force a dark palette, enlarge a tiny font — most everyday fixes are a few lines of CSS and take effect the instant the page renders.

JavaScript — your own logic

When CSS is not enough, a rule can run JavaScript. JustZix executes it in the page's MAIN world, so your script sees the real window object, the page's variables and its DOM — and it bypasses most Content-Security-Policy restrictions that block inline scripts. That is the difference between merely hiding an element and actually rewriting how a page behaves: add a keyboard shortcut, auto-expand collapsed content, watch for elements that load late.

Works even on Facebook, X and GitHub

Pages with a strict Content-Security-Policy (Facebook, X, GitHub and many more) block inline-injected scripts and new Function calls. JustZix gets through that wall with a three-tier strategy: it first tries to run your code via chrome.userScripts (which bypasses CSP without exception); if that is off, it falls back to a classic new Function; as a last resort it injects the script as <script src="blob:…"> — a form most policies allow. Your rules, actions and TEMP JS windows therefore run where most userscript extensions give up at the first step.

The userScripts path has to be enabled once in your browser settings ("Allow user scripts" or developer mode) — the extension shows exact instructions whenever a page proves unreachable by the other paths. The rest is automatic: JustZix picks the best available path on every site.

No account, no permission needed

Injection is entirely local. Rules live in your browser, run only for you, and need no approval from the site's author. There is no account to create and nothing to pay. You decide what runs and where, and you turn it off the moment you no longer need it.

Ready-made CSS and JS rules for popular sites are waiting in the examples catalog — copy one, adjust it, and you have a working rule in under a minute.