Characters entered with compose key on Firefox 90 disappear

[jams2]

Describe the bug

Originally shared in https://wagtailcms.slack.com/archives/C81FGJR2S/p1627024765193700

Running Firefox 90.0.1 (64-bit) on Linux.

Characters created using the compose key (for example, "compose-el-dash" for £), appear momentarily before disappearing. Copy-pasting one of these extended characters into the draftail editor works fine.

Tested against the draftail.org demo, the draftail storybook on a local install of this repo, and rich text fields in wagtail 2.13, 2.12, 2.11, 2.10 and 2.2, all with the same behaviour.

Behaviour is normal (I am able to enter characters using compose sequences) on the draftjs.org demo.

Some links about compose sequences:
https://fsymbols.com/keyboard/linux/compose/
https://man.archlinux.org/man/XCompose.3.en

Note: I was able to reproduce this using compose key sequences, but the original reporter of the issue on slack didn't specify if they were using this or another input method.

Which terms did you search for in the documentation and issue tracker?

firefox, accents, compose key, special characters

[fixgoats]

Also having this issue on Firefox 102 on Arch Linux. The demo on draftail.org correctly inputs and displays the accented character for an instant but then deletes it. Copying and pasting the character works. The draftjs.org demo behaves correctly. This bug makes draftail on Firefox unusable for writing many languages, including Icelandic.

[cfinnberg]

Don't like too much the me too messages, but here we go...
Same problem here with same actors Linux (Manjaro) and Firefox (106.0.4). In Windows seems to work fine.

Don't know if it helps, but @fixgoats added an interesting bit of information in the similar issue in Wagtail: wagtail/wagtail#7386 (comment)