It can be done using below steps:
1)Please update the browser to the version 53 and above.
Given is the link to download the same: https://www.mozilla.org/en-US/firefox/new/?scene=2
2)Download Click2Dial add on and add to Firefox.
3)Type About:Config in new tab of the Firefox browser.
• Right click on the page ->Select New-> Add Preference name as : “plugin.load_flash_only” as Boolean and set the value to false.
once, these steps are done, make a call.
Surely you will be able to make a one.