This detection is for several potentially unwanted modifications (PUMs) on user.js, a Firefox browser configuration file, where the installation of any third-party add-on or extension to Firefox is allowed.
The following string is modified in user.js:
Malwarebytes automatically deletes the user.js file that triggers the detection of PUM.Optional.FireFoxSearchOverride. Also, we advise users to do a full system scan as PUM.Optional.FireFoxSearchOverride could have been added to the system by malware or PUP.
When a PUM is detected on your computer, Malwarebytes for Windows does not know if it was authorized. Optimization software, malware, and Potentially Unwanted Programs (PUPs) are known to make these types of changes, hence they are regarded as potentially unwanted.
To have Malwarebytes for Windows ignore a PUM, you must add the PUM as an exclusion.
When a PUM is excluded, Malwarebytes for Windows does not detect the PUM during scans or Real-Time Protection.