So, this is a fork of YouTube Video and Audio Downloader (Dev Edt.) however:

1. Upon installation
File not found

Firefox can’t find the file at moz-extension://1a59976e-af26-48a2-8dcc-a73127056e13/null?version=0.9.3&type=install

2. Downloading doesn't work: Cannot detect something blah blah

3. Multiple strings are not populated.

Don't publish the alpha/debug versions of add-ons please. Test it first.