Dark themes are not consistentently executed on Linux Mint XFCE (22.2 Zara)

Hello there, I am new to this Linux thing and I have no idea if this is the right place. But in my new linux mint XFCE installation it seems, that dark themes are not persistent. Not sure if its a theme bug, a xfce bug or a linux kernel bug but I haven't found my problem with an online search and wanted to make the mint devs aware.

So I tested with multiple themes and it seems to be a consistent bug that when I choose a dark theme it will be persistent for thunar and most system apps but not apps like e.g. firefox (native) or flatpak apps like bitwarden.

Here are a couple pictures:

This is my firefox in a light theme ->

This is my firefox in a dark theme I like ->

And this is my firefox after restarting it (without changing the theme) ->:

The same is also true for apps like bitwarden (flatpak) and some other apps I tested. Again I am not sure what exactly the bug is and I am sorry if this is the wrong place. I also only tested on XFCE not sure if it also happens in the other flavours.

The report identifies XFCE on Linux Mint and reproduces the behavior in Firefox and Flatpak Bitwarden, but names no source file or test. First reproduce the theme reset after restarting Firefox and a Flatpak app, then determine whether mint-themes owns the behavior. Done means the responsible scope is identified and dark-theme persistence works consistently in the affected apps.