Providers are can offer this functionality for free to their customers.
For Microsoft Internet Explorer
Download Now the installer.
You have to download the module according to the installed Firefox version:
Mozilla Firefox 2.x module is available here.
Mozilla Firefox 3.x module is available here.
To install the VoipNow Browser Module for Firefox simply drag and drop it on the Firefox browser window.
The plug-in monitors the HTML pages opened in the browser and whenever it identifies a phone number, it replaces it with an interactive object that can be clicked in order to start a call to that number.
The browser plug-in works together with a 4PSA VoipNow Call API account. Any user that has a phone extension account on a 4PSA VoipNow server can download and use 4PSA VoipNow Browser Module.
Call API must be activated on the VoipNow user account setup in VoipNow Browser Module. For more details on how to activate Call API you should
read this article.