test: fix ontrack test
test: fix ontrack test

the ontrack test failed in Edge because it returned 8 results
instead of 7. The correct number of tests to pass is 8 if
getReceivers() is supported.

This re-enables the test in Firefox as well.

xdumaine/adapter,Acidburn0zzz/adapter,jan-ivar/adapter,Acidburn0zzz/adapter,webrtc/adapter,jan-ivar/adapter,Acidburn0zzz/adapter,xdumaine/adapter,webrtc/adapter