When you have multiple playback devices, the Windows system lets you to choose which one is the default. Usually, sounds from most programs will be played on that device if there is no specific customized settings in these programs. However, sometimes you may notice that when you tries to listen to streaming music/video from your web browser, the sound is directed to another device other than the default one set by Windows.
Actually, this may not be the problem of the browser, if the streaming content is played by a Adobe Flash-based player. In fact, the Flash player has its own setting for the playback device. To access it, right click on the Flash content in the webpage, and select “Settings…”. You will see a small window popping up. Select the Audio Output tab, and choose the audio device you want to use. Now the sounds in the Flash content will be played through the device you just selected.