A script that breaks the trick to detect opening developer tools for Firefox and its forks.
First of all, you need to change some settings in your browser.
In about:config, set devtools.toolbox.host to window and toggle devtools.debugger.skip-pausing to true.
Then install Tampermonkey and install the script from this link.
If you find sites that are still detected, feel free to raise an issue.
This script has no effect on Chromium-based browsers.