SurfingKeys is another such extension and my favorite one. In addition to the Vim like controls, it supports ton of additional functionality, including editing content in a small Vim like editor with I when needed (:wq will close popup window and update the text in the edit field), supports Vim marks with m, copy url with yy or many other clipboard related stuff, is configured in JavaScript, so you can access to anything what the browser does directly.
BTW screenshots were taken by opening the help with ? (Shift+/) on a webpage, and then using the its own screenshot capability to capture scrolling element yS. Which will only capture this element, not the entire webpage, in this case the help.
That's not the conclusion I have. The code is corrected and even if you don't trust the dev, the code is open and problems can be detected. It would be a problem if the developer did not acknowledge and correct the problem. It's 2 years ago and since then there wasn't an issue. But everyone can decide for themselves, I'm just speaking for myself.
While the code being open is good you still have to rely on trust.
I certainly don't have the time to review to code of each extension I use. And even then, we have no garanties that the extension distributed through the browser stores has the same code.
You can see the issue was opened on august 18th but the responsible commit was only made on the 19th. So the code was pushed the extension users before it was made available on the repository. Open code is of no help here.