After setting the options in my previous mail to false i found firefox still was downloading binaries of libgmpopenh264.so and libwidevinecdm.so.
I looked into the firefox sources (64.0~b12-2), and the installation seems to be done by toolkit/mozapps/extensions/internal/ProductAddonChecker.jsm by ProductAddonChecker.getProductAddonList(). There is a config option GMPPrefs.KEY_UPDATE_ENABLED to disable this, which is defined in toolkit/modules/GMPUtils.jsm line 118. Setting this to false seems to disable the binary blob downloads. So in /etc/firefox/firefox.js (debian/browser.js.in in the source), the option pref("media.gmp-gmpopenh264.enabled", false); should be changed to pref("media.gmp-manager.updateEnabled", false); Users needing to enable the EME and OpenH264 binaries can still change this option in about:config. Ingo -- ╭─╮ Kennedy's Lemma: ╭│───╮ If you can parse Perl, you can solve the Halting Problem. │╰─│─╯ ╰──╯ http://www.perlmonks.org/?node_id=663393