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Rated 4 out of 5 stars
I experienced the same problem as above, and found out that probably the ones who cannot install it (as I couldn't) actually already have it in the search bar.
There is a misunderstanding for many of us are looking for the equivalent of the chrome extension 'google dictionary' which works in the browser by popups and with a separate searchbar. This extension is a (however nicely working) search plugin.