Firefox theming issues in KDE

I recently got into the KDE world for some testing of Snap outside Ubuntu. And I chose KDE-Neon to start with. Now, firefox there is installed as an apt package by default. I also installed the snap package, because the apt package have some issues with plasma-browser-integration and needs some changes in apparmor. Now, the biggest issue there was theming. I installed an application style called Breeze-Black. Even though, the apt one was able to recognize it, the snap didn’t recognise it at all. Now, because I am new to KDE, I didn’t have much idea on how to investigate this, but I’d like to. Can the community give me sme insight. Here are some infos I got.

Snap Version

Apt Version

Now, from these screenshots, one can see that the apt version is using Breeze / Adwaita theme (dark and light ?? ) and the Snap one is using only Breeze / Breeze. But, still snap one is using default Breeze Dark, whereas the apt one is using Breeze Black. Any suggestions, on what should I try, and if this is a bigger problem with snaps as a whole?

Are you trying it under Wayland. If yes then this other user posted about the issue:

Although I notice you mention Breeze Black and there isn’t that one in the gtk-common-themes. There are only Breeze and Breeze Dark.

Can’t I use any aribatary theme? Is there no way? How does the snap of firefox looks for that theme? And yes, breeze black is a third party theme

No you can’t.

Snap has to connect to snap packaged version of the theme.

There was a concept of greedy plugs, used for theming which could solve this, perhaps. I am not knowledgeable enough on this aspect of desktop integration to be sure, but perhaps @jamesh or @zyga can help