Please follow the instructions below to unblock 3rd parties:
1) On the menu bar, click on the Firefox menu, select Options and select Preferences
2) Select the Privacy panel.
3) Set Firefox will: to Use custom settings for history – from the dropdown options
4) Make sure Accept Cookies from sites, and, Accept third-party cookies boxes are checked
5) Reload your CRM account.
You should now be able to play back your voicemail messages.