*.fb2 is an e-book format: http://en.wikipedia.org/wiki/FictionBook *.fb2.zip extension is widely used by online libraries and e-book readers (directly), because *.fb2 is plain xml, and the compressed version is much smaller. *.fb2 has application/x-fictionbook+xml mimetype. Some readers declare support for application/x-zip-compressed-fb2 mimetype, but it does not exist in shared-mime-info: http://git.openinkpot.org/fbreader.git/tree/fbreader/desktop/desktop http://crengine.git.sourceforge.net/git/gitweb.cgi?p=crengine/crengine;a=blob;f=cr3gui/data/desktop/cr3.desktop No standart mimetype for *.fb2.zip files blocks support for opening such files in KDE/Okular (because no backend/generator could be associated with *.fb2.zip files).
See: http://cgit.freedesktop.org/xdg/shared-mime-info/tree/HACKING about adding new mime-types.
Created attachment 90606 [details] [review] patch
commit fe0ce0f210bdd39bcba1d6301e535ab29fc94b91 Author: David Tardon <dtardon@redhat.com> Date: Wed Dec 11 14:07:39 2013 +0100 add mimetype for compressed FictionBook2 https://bugs.freedesktop.org/show_bug.cgi?id=45795
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