when ever i play a video in firefox, the output form my speaker is low?

whenever i play the audio or video, in audio mixer(windows 7 64bit) firefox show 100% but when it come to speaker it shows 60%. but when i play the same audio using other browser it is perfect both of them show correct value. what is the issue?? and also when ever i try to play video it take long time to load up, it says "if video is doesn't startup try to restart the device" this issue happen recently only before that video start without any issue.. is there any solution.