The #Firefish word #trademark is registered for NICE classes 9, 41, 42, i.e. computer software and services etc., for the whole of the European Union (and I believe for the UK too, not checked). Server admins in those jurisdictions, you may want to avoid domains containing the word or at least get legal advice before deploying a server with such a domain - this could potentially be costly otherwise.
@choyer@sin@fediversenews to add one more example: gmail.pl was registered to some person and hosted a website for book lovers (that translated into gmail acronym). Court in Poland denied the claim to this domain and Google eventually paid him.