windowrulev2 title matching does not work for Betterbird compose windows

[Peter111160]

Hi everyone,

I’m trying to float (and optionally pin) the compose window of Betterbird (Thunderbird fork) in Hyprland using windowrulev2.

The relevant windows are titled e.g.:

• Verfassen:
• Antworten:
• Weiterleiten:

---

What works

Matching by class works perfectly:

windowrulev2 = float, class:eu.betterbird.Betterbird

→ All Betterbird windows float as expected.

---

What does not work

Any rule involving title: does not match, even with very simple patterns:

windowrulev2 = float, title:Verfassen:
windowrulev2 = float, class:eu.betterbird.Betterbird, title:Verfassen:
windowrulev2 = float, title:^(Verfassen:|Antworten:|Weiterleiten:)

---

hyprctl clients output (compose window)

class: eu.betterbird.Betterbird
title: Verfassen: Re: <subject> - Betterbird
initialClass: eu.betterbird.Betterbird
initialTitle: Verfassen: (Kein Betreff)
xwayland: 0

---

Additional notes

• windowrulev2 itself works fine in general (e.g. class-based rules work reliably for applications like Thunar).
• For Thunar, only class: matching is used; no title: matching is required there.
• Betterbird is running native Wayland (xwayland: 0).
• The issue appears only when trying to distinguish Betterbird/Thunderbird compose windows using title: matching.

---

System details

• OS: CachyOS
• WM: Hyprland (Wayland)
• Application: Betterbird 140.6.0esr-bb15
• Protocol: Wayland (not XWayland)

---

Questions

1. Are there any known limitations or quirks with title: matching in windowrulev2 for GTK / Mozilla-based applications?
2. Is there a recommended selector or alternative matching method for Betterbird / Thunderbird compose windows?
3. Should initialTitle be used or matched differently in this case?

Thanks a lot for any hints or pointers!