I got installed some software without my permission with K-lite codec pack on Windows 10. And the CIS successfully prevented changes in edge browser. But. some firefox settings have been changed (home page to Yahoo, and opening only the home page, not restoring the previous session and search settings - made Yahoo as default).
It is “K-Lite_Codec_Pack_1350_Basic.exe” with SHA256 194A5F5CA4B6B4FA57415AAC74C79C41FFF033B88A7AD239B0FA560C6E4B5188
it can be obtained here:
There is hidden install without any check-boxes - Ad-Aware Web Companion. And it is doing it’s “protection”. I got CIS 10 HIPS in safe mode - no reaction to install, only to changing configuration of edge browser. And suddenly noticed Firefox being stopped and restarted with configuration changes.
It seems Codec installer shows different offers based on system, i could not see offer for Web Companion so tried to install Web Companion from their website that does offer Yahoo.
I did see CIS alerting for change in Firefox.
We will see if we can see offer you observed, quite possible there is an intermediate binary being installed that does the trick.