Extension is not built correctly when git is missing from PATH

[automatedbugreportingfacility]

As I was building extensions (Windows 7, "node make firefox") to bisect #5400, I noticed that when "git" is not an environmental variable, a broken extension is generated due to following code in pdf.js and pdf.worker.js:

PDFJS.build = ''git' is not recognized as an internal or external command,
operable program or batch file.
';

With this string fixed, the extension worked alright. Would it be possible to fall back to some valid string for "PDFJS.build" if git is missing from PATH?

[Snuffleupagus]

Given that the Firefox addon was removed in PR #9566, this issue can probably be closed now.