Dorico uses the audio engine from Cubase which requires very low level access to the soundcard in order to provide low latency playback. If you have a soundcard that has native ASIO drivers then the audio engine can access the device hardware directly, which will give you the best results.
However, if your PC has a standard on-board soundcard then this doesn't provide this low level access, so the audio engine has to use a component called the ASIO Generic Lower Latency Driver. This is a compability layer that tries to gain exclusive access to your soundcard so that it can get the lowest latency that it can.
This can conflict with other applications that are playing audio, such as the web browser or media player.
Please go to the Generic Lower-Latency ASIO Driver settings in Dorico via Edit > Device Setup > Device Control panel and turn off the checkbox labelled "Allow ASIO host application to take exclusive control of selected port configuration" which allows both applications to play audio at the same time.
However, for the best results we recommend the use of soundcards with native ASIO driver support.