It's my understanding that the usage of the debugger is detectable by scripts running on the page. I've actually come across content websites that will refuse to activate their features (play video) if the debugger is active.

Similarly on Android some video streaming apps will refuse to load and play their content catalog if USB debugging is enabled.

A javascript file, whose name changes with every refresh, is loaded. The script calls the `debugger` keyword, which only functions when you have DevTools open.

Meanwhile, a tickers is running. If a tick takes too long, it interprets that as the debugger having been called.

    <script>
        setInterval(function() {
            try {
                let before = new Date().getTime();

                // This will pause the program execution if debugging is enabled.
                // If debugging isn't enabled this statement is a no-op.
                debugger;

                let after = new Date().getTime();

                // Detect if the program was paused or not.
                if (after - before > 0.01) {
                    // > 10ms difference?  The program was (most likely) paused by the debugger.
                    document.body.innerHTML = "<h1>Debugging started</h1>";
                }
            } catch(e) {}
        }, 1000);
    </script>

I think you’re probably right that it wouldn’t detect presence of your extension, since that code runs in its own context and I assume doesn’t actually call the debugger. If your extension injects a script into the page, then that could be detected with this technique or similar.

This method and a few others are described in this paper: https://www.usenix.org/system/files/sec21-musch.pdf

The debugger timing method is described on page 10.

"Vytal" started debugging this browser

Is there a way to get rid of it?

This should work

chrome.exe --silent-debugger-extension-api

Is it safe to do? I mean I want to stop this message for Vytal only, because I know that it uses debugger API. But I would want to know if tomorrow my adblocker starts to use debugger API.

For example:

https://wikishootme.toolforge.org/

I don’t believe this is possible in client JavaScript within a web browser. Very open to be proved wrong.

(FWIW, a website that is given media recording privileges can definitely do that, though, using WebRTC. If you don't have that privilege then you can still use the WebRTC API but it doesn't return alternative candidates. But I also don't think that is what they meant.)

There are services that wardrive around mapping locations of WiFi access points. Your laptop periodically will phone home with your nearby Wi-Fi MAC addresses (BSSIDs) to ask where they were detected.

Here's one such service: https://www.skyhook.com/wifi-location-solutions

When Location Services is on (which it is by default), macOS will periodically switch your wireless card to monitor mode to find those nearby SSIDs. That briefly interrupts normal network traffic.

IIRC, it does this more often when Find My.app is turned on.

You can disable Location Services in: System Preferences > Security & Privacy > Location Services

: if you're on Android, you'll need either an unstable version (Beta, Nightly) or a fork (Fennec from F-Droid) of Firefox to get access to that page because Mozilla decided users of the standard distribution can't be trusted with these settings.

https://www.expressvpn.com/webrtc-leak-test

https://www.dnsleaktest.com/

http://ipv6leak.com/

Most of my linux desktop usage these days is stuff like writing scrapers in cloud containers that need a real browser that I can control using selenium or puppeteer or whatever though, is it supporting anything like that? If this works on Windows too that would be a bonus.

Doesn't Mozilla's revenue breakdown still show Google as the majority of their revenue, and pocket et al are efforts to diversify?

You can literally accomplish this in firefox by other means.