alt Hacker NewsProbably because there often isn't a straight answer to that. I've no idea about the progeny of this browser, but I've seen several Firefox forks "interbreed", borrowing patches and feature backports from each other. So there might be a specific version of Firefox you can ultimately trace the repo to, it likely has code from newer versions spliced in. At least, that was my impression.
The closest they say is:
PowerFox is both standards compliant and feature-rich, supporting the latest web technologies to ensure compatibility with modern websites.
which means.. next to nothing. No "PowerFox version X has (at least) the same web standards support as Firefox Y".
it likely has code from newer versions spliced in
That's a good thing, but making it clearer what to expect will make it easier for potential users to decide whether to give it a try.