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Try disabling add-ons. 
You can click "download full resolution" to download the highest resolution provided by the uploader. 
If the image you like is in the gallery, you can upvote it and it will be saved to your "liked" folder. Otherwise there is no way to do that. 
The editor is working normally. Try disabling add-ons and making sure your browser is fully updated. 
Email support@imgur.com with your account information. 
I don't know, but maybe it got reported or it got too many downvotes.