I have been moving round trying to use the manual method still do not work, what I did was to delete it to see if I could download it back (add) but it refuses. Seems there is no hope for that, I am only window store now downloading my firefox to see if I can use it on that browser.
Have you tried downloading it from here?
You can try re-downloading and installing this [
Extension] by enabling Developer Mode, and let me know the results.
Then drag&drop it (with developer mode enabled) in the extensions management page
chrome://extensions/Here look, this is what I am seeing over here and there nothing displaying after I finished download extension as instructed.

This is after downloading the extension.. from my download history..

Then this is the extension management page, the developer mode is turned on and yet the extension do not display there.