Issue: A connection failure error is received when installing Mailtrack on Firefox.
Explanation: This error usually appears because of how Firefox is configured.
If you do as follows the error should disappear:
1) Copy/paste about:config in the address bar in Firefox then press enter.
2) Click the blue 'I accept the risk!' button.
3) Right-click anywhere on the page then New > String from the menu that appears.
3) In the text field in the window that appears, type xpinstall.enabled and click OK.
4) Type true in the text field provided then click OK.
5) Restart Firefox.