Firefox 52.5.0
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After restarting Firefox or even rebooting: copyfish icon greyed out.
Remove.

edit after reply:
Fair enough - I'll try the older version.
The 1 star is there because there's no zero star: meaning it does nothing.
I must add that Copyfish does work on Chrome, but until I get the full hang of it I'll refrain from giving one or more stars there. Besides I work in FF and only revert to Chrome if everything else fails.

edit2: It turns out it was not an older version, but a newer version where you have added support. Kudos to you for doing that.
However my one star was well deserved then. For there was nothing in the version history that even hinted at previous versions not being supported. Nor is/was there a requirements part.