Build against GStreamer 1.0 by default on Linux

During playback of mp4 videos I only see a white screen. Firefox on the same machine works fine. Also, webm videos work. Steps to reproduce: create an HTML document with the following content:

<!doctype html>
<html>
<head>
</head>
<body>
<video src="video.mp4" controls >
</video>
</body>
</html>

Put an mp4 file next to the document and open it. Tor browser version 5.0.6.

Trac:
Username: slycelote

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