Apparently, the Gnome desktop environment for Linux systems has an issue with handling some user-specified default application choices. When using Zotero in Ubuntu, therefore, it may be necessary to edit /etc/gnome/defaults.list manually in order to have Zotero default to a PDF viewer besides Evince (e.g., Okular). Changing the “application/pdf=evince.desktop” line in this file to reflect the desired PDF viewer default (e.g., “application/pdf=kde4-okularApplication_pdf.desktop”) seems to do the trick, however. For more information, please see Zotero’s help forums and knowledge base.
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