This extension adds a simple stereo audio panning slider on a per tab basis. I couldn’t find an existing free extension that works for multiple tabs at once so I whipped this up in a few short moments for my own use. If you can make use of it as well then by all means go for it!
Source Code: https://github.com/1215drew/AudioPan
=== Version 1.2 update ===
Fixed a mistake that only allowed 80% audio panning. Now you can pan 100%
Credit to davidschlachter