  Digital harms are widespread in the mobile ecosystem. As these devices gain
ever more prominence in our daily lives, so too increases the potential for
malicious attacks against individuals. The last line of defense against a range
of digital harms - including digital distraction, political polarisation
through hate speech, and children being exposed to damaging material - is the
user interface. This work introduces GreaseTerminator to enable researchers to
develop, deploy, and test interventions against these harms with end-users. We
demonstrate the ease of intervention development and deployment, as well as the
broad range of harms potentially covered with GreaseTerminator in five in-depth
case studies.
