Comment 6 for bug 1959027

Created attachment 9262422
Screenshot 1: Wrong theme, UI font too big

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:96.0) Gecko/20100101 Firefox/96.0

Steps to reproduce:

I initially filed this bug on Launchpad and was encouraged to open a report on the Mozilla bug tracker. Link to my original report:
https://bugs.launchpad.net/bugs/1959027

1. Install Kubuntu 22.04 daily-live image (Firefox ships as Snap)
2. On login screen of SDDM (Display manager), select "Plasma (Wayland Session)"
3. In Plasma Systemsettings, switch Global Theme to "Breeze Dark"
4. Launch Firefox (with fresh profile)

Actual results:

1. Firefox uses a light theme instead of a dark one, logging out and in again is required to make Firefox use a dark theme.
2. Font size of the UI elements is too big.
3. Wrong GTK theme is used (Adwaita, instead of Breeze Dark).
4. Mouse cursor uses wrong theme and is too big (it changes, when moving in and out of the Firefox window).
5. Wrong file dialogs (e.g. 'File -> Open...') are used (from GTK instead of KDE). UI text in file dialogs is rendered in a strange jagged/distorted way.

(Screenshots attached)

Expected results:

1. Firefox should immediately use the dark theme without requiring to log out and in again.
2. Font size of UI elements should be the same as on all other applications.
3. Firefox should use Breeze Dark (or Light) as GTK theme on Plasma.
4. The mouse cursor should look the same as in all other applications.
5. Firefox should use KDE file dialogs (without jagged/distorted font rendering).

None of these issues happen:
* When I run Firefox as Snap in Plasma X11 session.
* When I run Firefox as Deb (both Plasma Wayland and X11 session work fine).
So it seems to be specific to running the Firefox Snap under Plasma Wayland session.