Fcitx5 IME with preedit composition not working in Firefox

[bczhc]

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Does the issue happen when logged out?

Yes

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Yes

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Account name

bczhc

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Current Behavior

Can't start typing using Fcitx5 input method, with "preedit" composition mode. It's OK when preedit is disabled.

Expected Behavior

Type normally.

Steps To Reproduce

1. Set up Fcitx5 IME and add an input method that needs composing (like Chinese or Japanese). In this case I'm using fcitx5-rime with schema "朙月拼音".
2. Go to Monkeytype with Firefox.
3. Select the input language to the desired one. I use "Chinese Simplified".
4. Toggle the input method (the shortcut I'm using is Super+space) and start typing.
5. Observed: The composition view won't show, and it's still typing alphabets.

Environment

• OS: Arch Linux rolling; kernel 6.11.0-modified-dirty.
• Browser: Firefox
• Browser Version: 131.0

Anything else?

Screenrecord demonstration:

https://github.com/user-attachments/assets/8b26971d-7133-47b1-9d98-d29c0ae217d1

[SajanGhuman]

Weird, I also happen to be using fcitx5 with arch. I have "preedit" enabled in Firefox but not facing this bug. I am using Punjabi language which uses composing though it is relatively straightforward to type.