This looks fine in the latest stable chromium on bionic (and in the snap too). See attached screenshot. The only place where the rainbow is not rendered correctly is in the tab handle, but that's a different issue than the one originally reported.
** Attachment added: "chromium-rainbow.png" https://bugs.launchpad.net/ubuntu/+source/thunderbird/+bug/1779569/+attachment/5173096/+files/chromium-rainbow.png ** Changed in: chromium-browser (Ubuntu) Status: New => Fix Released -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to chromium-browser in Ubuntu. https://bugs.launchpad.net/bugs/1779569 Title: 🌈 looks odd in thunderbird, chrome/chromium, okish in firefox Status in Mozilla Thunderbird: Unknown Status in chromium-browser package in Ubuntu: Fix Released Status in firefox package in Ubuntu: New Status in thunderbird package in Ubuntu: New Bug description: New install of 18.04 and thunderbird is showing weird images in odd places for some email. See screen shot for example. In this case it is a weird rainbow, but I have also seen other things like a big stop sign and other strange stuff. Emoji support is inconsistent: - google chrome title is good - firefox title is good - google chrome contents, is bad, black&white ascii icon - fiefox contents, is ok, not the same icon as in the title - thunderbird content is ok, but too huge To manage notifications about this bug go to: https://bugs.launchpad.net/thunderbird/+bug/1779569/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : [email protected] Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp

