The Mintcast PUPs use the way Firefox loads its settings to make some changes that the user is not aware off and that put him at extra risk by disabling the safebrowsing settings. Shell&Services and Mintcast 3.0.1 are Mintcast variants which make some annoying changes on your system if you are a Firefox user. The use of the user.js file is not an original idea by Mintcast. Other Potentially Unwanted Programs (PUPs) like those of the Yontoo/BrowseFox family have also been known to add a user.js file. If you restart Firefox after re-checking those. boxes, you will find the checkmarks are gone again.”]
Source: https://blog.malwarebytes.com/puppum/2015/12/mintcast-pups-disable-safebrowsing-settings-in-firefox/