Hello Martin. Thank you for the information. Please follow the instructions to remove the add-on from the Firefox browser.
(1). Click on the button at the top right corner to open Menu > Add-ons > Extensions > (2). Find Search.mymapsxp.com related add-ons and delete them. Note: it’s better to remove anything you don’t need or trust especially those installed recently. Please feel free to contact us back for any further assistance.