Erewhon

I've noticed this problem when I've used CCleaner a few times now - Analyzing my computer for cookies, etc. shows over 124 MB of unwanted files and other stuff (currently). After I click 'Clean' the CCleaner only cleans maybe 4 MB of stuff, leaving the rest untouched. Even after several tries, only a couple of MB are cleaned up each time. I use a Macbook Pro with MAcOS Sierra 10.12.5. I should add that my browser is Firefox 54.0 and it is where most of the uncleaned files are coming from.