Visit Chrome Web Store to get FreeTheTree extension (a.k.a. plugin, addon).
Click on a “+ Free” or “+ Add to Chrome” button, a notification pop-up will ask you to confirm that you want to add the extension to Chrome.
Click “Add” and the browser should automatically download and install the extension.
After successful installation additional features will be available in Manage my ads section on Gumtree.
There is also a Firefox version available in Add-ons shop