Hi Natascia, have you checked your Control Panel for Radsteroids adware? In some cases this adware doesn't install it's plugins to Internet browsers so it should be enough to uninstall it's app from Control Panel.

If you can't uninstall it try using third party tools:

CCleaner
Download, install and run CCleaner. After launching the program select "Tools". In the uninstall programs list select the program you want to uninstall and click the "Run Uninstaller" button.

Revo Uninstaller
Download, install and run Revo Uninstaller. After launching the program select the program you want to uninstall from the list and click on the "uninstall" button.

IObit uninstaller
Download, install and run IObit Uninstaller. After launching the program select the program you want to uninstall from the list and click on the "uninstall" button.

After uninstalling radsteroids you should also scan your computer with Malwarebytes Antimalware and Spyhunter, both of these programs are capable of detecting and removing radsteroids - https://www.pcrisk.com/top-spyware-removers