Fix sourcemaps in JSXTransformer for Firefox

[zpao]

Fixes #1725

[sophiebits]

I don't understand this sentence.

[zpao]

Firefox has problems when the sourcemap source is a proper URL with a protocol and hostname, so just use the path.

I'm assuming you meant the next one.

Things seem to work fine if we just use filename.js instead of path/to/filename.js, but ...

So given http://hostname:port/path/to/filename.js, we have to strip it down to path/to/filename.js at least. We could strip it all the way to filename.js, which also works (and is what I originally tested). The potential downside (I didn't back this up with a test) is that there may be path/to/filename.js and otherpath/to/filename.js on the same page and I thought perhaps the devtools would get confused mapping them back from the sourcemap if we just used filename.js

[sophiebits]

Things seem to work fine if we just use filename.js instead of path/to/filename.js

This sounds to me like "I want to use just filename.js but I can't". I guess it seems obvious enough to me that having the path is better if it works – will anyone see .pathname.substr(1) and ask, "why isn't that just the filename?"? At any rate, maybe:

We could use just the filename, but hopefully using the full path will prevent potential issues where the same filename exists in multiple directories.

[zpao]

I'll take your rephrase.