Unfortunately because of problems I faced to publish this extension to Chrome Extension Web Store or Microsoft Extensions Store, I had to only publish and leave it here on Github.
Download release file suitable for your browser, and drag and drop downloaded file into the browser.
When you're on payment page, just click on extensions icon in the tab bar, the extension will automatically validate payment gateway and show you the results. Easy.
Well, the project is open-source, so you can take a look at the source code. You can also inspect element the extension and navigate to it's installation folder and check out the code running by the extension right there. So no hands behind the curtain. 🙌
Sure. My first intension was to publish this extension along with being open-source project. But as I'm writing this readme file now, I'm limited by my countries sanctions, so I just published it as open-source project on GitHub. I appreciate your contribution. So YES.