If you keep receiving the activation pop-up when trying to install and activate Mailtrack on your email account...
...then we have a solution:
1) Copy/paste chrome://settings/resetProfileSettings in the address bar in Chrome and press enter.
2) Reinstall the Mailtrack extension on your browser (instructions explaining how to do this can be found here).
Reinstall Mailtrack by doing as follows:
1) Go to the list of add-ons and extensions in Firefox, find the Mailtrack extension and click the option "Remove".
2) Then, head over to https://mailtrack.io/en/install-firefox-extension.
3) Click the "Install" button and follow the process to install the latest version of Mailtrack.
4) Go to Gmail and refresh the tab a couple of times.