1. Ensure your network ports aren’t being blocked by Firewall / router / antivirus software. (Refer: Firewall and port settings)
  2. Confirm the hardware is correctly attached and ensure the correct microphone and speakers are selected in software settings.
  3. Check to ensure the microphone is not muted (some have a hardware mute button) and the speaker volume is turned up.
  4. If you are using a bluetooth headset, use a USB dongle instead of relying on the computer’s native bluetooth. Retry with a USB headset or a 3.5mm headset and compare the call quality. Since each device behaves differently with each browser, it can be more than a little trouble to tackle such hardware related issues.

For more information about improving call quality, please refer to this article.