Put a gentle "Use Firefox" (or any other non-Chromium-based browser) message on your website. It doesn't have to be in-your-face, just something small.
I've taken my own advice and added it to my own website: https://geeklaunch.io/
(It only appears on Chromium-based browsers.)
We can slowly turn the tide, little by little.
<span id='browser' class='hidden'>
This website is designed for <a target="_blank" rel="noopener noreferrer" href="https://firefox.com/">Firefox</a>, a web browser that respects your privacy.
</span>
<script>
if (window.chrome) {
document.getElementById('browser').className = '';
}
</script>
Class .hidden must hide the element somehow, in this case I do: .hidden { display: none; }1. Instead of using CSS to hide it by default, make the script to only add it (perhaps by document.write, or alternatively by adding text to an empty <div> or <span>) if Chrome is detected. (This way it will be compatible even if CSS is disabled (or not implemented).)
2. Instead of Firefox, mention something else such as Line Mode Browser (it has some features I had not seen in other web browsers, but which I think are good and would like to have), or some other uncommon one which doesn't have Google and Mozilla etc, or more than one.