I think, it is an problem with an media codec which I updated in the last days but I don't know, which. The problem is, I see a black screen, the video is loading but dosn't start to play. Portage 2.3.0 (python 3.4.5-final-0, default/linux/amd64/13.0/desktop/plasma/systemd, gcc-5.4.0, glibc-2.23-r2, 4.7.0-gentoo x86_64) ================================================================= System uname: Linux-4.7.0-gentoo-x86_64-Intel-R-_Pentium-R-_CPU_B960_@_2.20GHz-with-gentoo-2.2 KiB Mem: 3902832 total, 285980 free KiB Swap: 8191996 total, 8191192 free Timestamp of repository gentoo: Wed, 03 Aug 2016 04:00:02 +0000 sh bash 4.3_p46 ld GNU gold (Gentoo 2.26.1 p1.0 2.26.1) 1.11 app-shells/bash: 4.3_p46::gentoo dev-java/java-config: 2.2.0-r3::gentoo dev-lang/perl: 5.24.0-r1::gentoo dev-lang/python: 2.7.12::gentoo, 3.4.5::gentoo dev-util/cmake: 3.6.1::gentoo dev-util/pkgconfig: 0.29.1::gentoo sys-apps/baselayout: 2.2-r1::gentoo sys-apps/openrc: 0.21.3::gentoo sys-apps/sandbox: 2.10-r2::gentoo sys-devel/autoconf: 2.13::gentoo, 2.69-r2::gentoo sys-devel/automake: 1.11.6-r2::gentoo, 1.13.4-r1::gentoo, 1.14.1-r1::gentoo, 1.15-r2::gentoo sys-devel/binutils: 2.26.1::gentoo sys-devel/gcc: 5.4.0::gentoo sys-devel/gcc-config: 1.8-r1::gentoo sys-devel/libtool: 2.4.6-r2::gentoo sys-devel/make: 4.2.1::gentoo sys-kernel/linux-headers: 4.7::gentoo (virtual/os-headers) sys-libs/glibc: 2.23-r2::gentoo Repositories: gentoo location: /usr/portage sync-type: rsync sync-uri: rsync://rsync.gentoo.org/gentoo-portage priority: -1000 ACCEPT_KEYWORDS="amd64 ~amd64" ACCEPT_LICENSE="*" CBUILD="x86_64-pc-linux-gnu" CFLAGS="-march=native -O2 -pipe" CHOST="x86_64-pc-linux-gnu" CONFIG_PROTECT="/etc /usr/lib64/libreoffice/program/sofficerc /usr/share/config /usr/share/gnupg/qualified.txt" CONFIG_PROTECT_MASK="/etc/ca-certificates.conf /etc/dconf /etc/env.d /etc/fonts/fonts.conf /etc/gconf /etc/gentoo-release /etc/revdep-rebuild /etc/sandbox.d /etc/terminfo" CXXFLAGS="-march=native -O2 -pipe" DISTDIR="/usr/portage/distfiles" EMERGE_DEFAULT_OPTS="--with-bdeps=y" FCFLAGS="-march=native -O2 -pipe" FEATURES="assume-digests binpkg-logs candy config-protect-if-modified distlocks ebuild-locks fixlafiles merge-sync news parallel-fetch preserve-libs protect-owned sandbox sfperms strict unknown-features-warn unmerge-logs unmerge-orphans userfetch userpriv usersandbox usersync xattr" FFLAGS="-march=native -O2 -pipe" GENTOO_MIRRORS="http://distfiles.gentoo.org" LANG="de_DE.utf8" LDFLAGS="-Wl,-O1 -Wl,--as-needed" MAKEOPTS="-j3" PKGDIR="/usr/portage/packages" PORTAGE_CONFIGROOT="/" PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --omit-dir-times --compress --force --whole-file --delete --stats --human-readable --timeout=180 --exclude=/distfiles --exclude=/local --exclude=/packages --exclude=/.git" PORTAGE_TMPDIR="/var/tmp" USE="X a52 aac acl acpi alsa amd64 berkdb branding bzip2 cairo cdda cdr clang cli cracklib crypt cups cxx dbus declarative dri dts dvd dvdr emboss encode exif fam ffmpeg fingerprint firefox flac fortran gdbm gif glamor gold google gpm gtk iconv ipv6 jpeg kde kipi lastfm lcms ldap legacy-systray libnotify lm_sensors mad matroska mmx mmxext mng modules mp3 mp4 mpeg mtp multilib ncurses networkmanager nls nptl ogg opengl openmp opus pam pango pch pcre pdf phonon pim plasma png policykit postproc ppds pulseaudio qml qt3support qt4 qt5 readline sdl seccomp semantic-desktop session spell sse sse2 ssl startup-notification svg system-harfbuzz system-icu system-jpeg system-libvpx system-sqlite systemd tcpd threads tiff truetype udev udisks unicode upnp upower usb vaapi vc vorbis vpx widgets wxwidgets x264 x265 xattr xcb xcomposite xinerama xml xscreensaver xv xvid zlib" ABI_X86="64" ALSA_CARDS="ali5451 als4000 atiixp atiixp-modem bt87x ca0106 cmipci emu10k1x ens1370 ens1371 es1938 es1968 fm801 hda-intel intel8x0 intel8x0m maestro3 trident usb-audio via82xx via82xx-modem ymfpci" APACHE2_MODULES="authn_core authz_core socache_shmcb unixd actions alias auth_basic authn_alias authn_anon authn_dbm authn_default authn_file authz_dbm authz_default authz_groupfile authz_host authz_owner authz_user autoindex cache cgi cgid dav dav_fs dav_lock deflate dir disk_cache env expires ext_filter file_cache filter headers include info log_config logio mem_cache mime mime_magic negotiation rewrite setenvif speling status unique_id userdir usertrack vhost_alias" CALLIGRA_FEATURES="kexi words flow plan sheets stage tables krita karbon braindump author" CAMERAS="casio_qv" COLLECTD_PLUGINS="df interface irq load memory rrdtool swap syslog" CPU_FLAGS_X86="mmx mmxext popcnt sse sse2 sse3 sse4_1 sse4_2 ssse3" ELIBC="glibc" GPSD_PROTOCOLS="ashtech aivdm earthmate evermore fv18 garmin garmintxt gpsclock itrax mtk3301 nmea ntrip navcom oceanserver oldstyle oncore rtcm104v2 rtcm104v3 sirf superstar2 timing tsip tripmate tnt ublox ubx" INPUT_DEVICES="evdev synaptics" KERNEL="linux" L10N="de" LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses text" LIBREOFFICE_EXTENSIONS="presenter-console presenter-minimizer" LINGUAS="de" OFFICE_IMPLEMENTATION="libreoffice" PHP_TARGETS="php5-5" PYTHON_SINGLE_TARGET="python2_7" PYTHON_TARGETS="python2_7 python3_4" RUBY_TARGETS="ruby20 ruby21" SANE_BACKENDS="niash" USERLAND="GNU" VIDEO_CARDS="intel i965" XTABLES_ADDONS="quota2 psd pknock lscan length2 ipv4options ipset ipp2p iface geoip fuzzy condition tee tarpit sysrq steal rawnat logmark ipmark dhcpmac delude chaos account" Unset: CC, CPPFLAGS, CTARGET, CXX, INSTALL_MASK, LC_ALL, PORTAGE_BUNZIP2_COMMAND, PORTAGE_COMPRESS, PORTAGE_COMPRESS_FLAGS, PORTAGE_RSYNC_EXTRA_OPTS, USE_PYTHON
this is an FAQ, so I wrote a section in the wiki: https://wiki.gentoo.org/wiki/Firefox#HTML_5_video_support
