It is in fact a known bug, caused by versions of fontconfig < 2.13. See https://bugzilla.mozilla.org/show_bug.cgi?id=1566053 and https://askubuntu.com/questions/1076412/firefox-freezing-with-100-cpu- usage-for-30-seconds-when-launching-chromium#answer-1089841.
** Bug watch added: Mozilla Bugzilla #1566053 https://bugzilla.mozilla.org/show_bug.cgi?id=1566053 ** Changed in: firefox (Ubuntu) Status: New => Confirmed ** Also affects: firefox via https://bugzilla.mozilla.org/show_bug.cgi?id=1566053 Importance: Unknown Status: Unknown -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1856624 Title: Firefox freezes temporarily at 100% CPU when Chromium is opened To manage notifications about this bug go to: https://bugs.launchpad.net/firefox/+bug/1856624/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
