you might want to run a SFC (system file check) on your system.
I have found many so called 'helper' apps tend to do the reverse in the end as the can also (unintentionally) interfere with other uses.
There was a time, everybody (the sites) wanted to install
helper toolbars on your browser (data mine or site steerage or even plain ole malicious). The system got so bad that a higher end (for the time) one, crawled.
I run (to my knowledge
) pretty much Vanilla at the OS level and relegate the add-ons to specific apps like Sigil and Calibre.