Sometimes it's helpful to compare how two different projects implement the same feature. You can often learn a lot by reading the code in a project that does what you want, in order to make another do new things.

Read through both files and try to orient yourself. Don't get hung-up on understanding every single line, especially in the Firefox C++ code, which uses lots of internal string APIs and , [https://en.wikipedia.org/wiki/XPCOM XPCOM base code], etc. Instead, try to find clues as to how each one is doing what it does with input strings before converting them to URLs.