origin is here : https://bugs.kde.org/show_bug.cgi?id=341803 The desktop files needs %u instead of %U to work properly. probably a mistake made in these packages too : ? $ find . -name '*.desktop' | xargs grep -H '%U' ./mail-client/thunderbird/files/icon/thunderbird-unbranded.desktop:Exec=/usr/bin/thunderbird %U ./mail-client/thunderbird/files/icon/thunderbird.desktop:Exec=/usr/bin/thunderbird %U ./www-client/firefox-bin/files/firefox-bin.desktop:Exec=/usr/bin/firefox-bin %U ./www-client/firefox/files/icon/firefox.desktop:Exec=firefox %U ./www-client/seamonkey-bin/files/icon/seamonkey-bin.desktop:Exec=/usr/bin/seamonkey-bin %U ./www-client/seamonkey/files/icon/seamonkey.desktop:Exec=seamonkey %U ./x11-apps/whyteboard/files/whyteboard.desktop:Exec=whyteboard %U
Source packages are fixed in mozilla overlay and will be committed to main tree during next round of updates.
Thanks for reporting, all have been fixed.