Well, one difference is that "censure" is commonly used, and I don't think I've ever heard or read "fulminate" -- I had to look it up to verify that the basic meaning is similar. The other significant difference is that "censure" takes a direct object -- you censure a person, for instance. You don't "fulminate somebody" -- you fulminate against somebody, or possibly fulminate a decree against something.
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