How do I install add-ons? Descriptive way did not work

Hello,

I downloaded a couple add-ons for adobe muse. For example. Disable Scrollbaars, Right-click. I could not find the files in my download folder (mac ox 10.9.4).  I downloaded the add-ons and tried to install via extension manager. It did not work. I checked troublehshooting. I was asked to click in the adobe cloud button and to turn on file sync on. For some reason that I do not understand the file sync 'jumps' always back to 'off'.

Does anyone has an idea what I should do?

Thanks for response.