Electron App authors must stop overriding the native wm's window title bar, or when they do they should still offer the option of being able to switch to using the native title bar.
Even if you have the exact same extensions the fact that you have an old Firefox profile may be hindering the results. Try comparing with a fresh Firefox profile with the same extensions.
In such rare case, it would download the required version. Having two separate Electron versions is still better than having ten in total, for each app separately.
Another Electron app that isn't visually integrated with Linux -- under GNOME/Wayland the app does not have native or at least native looking window buttons, it also has sharp edges without a shadow behind the window, as all other apps.
This is a surprise as Podman Desktop development is lead by RedHat, a company not only behind a Linux distro but one that leads the GNOME project.
You can also add [Desktop action ...] sections to your .desktop file for each profile, this will add new right-click/context menu options for easy launching of the profiles from your Linux dock.
Lack of an option to have the address bar at the bottom near the keyboard like on Safari, lack of address bar gestures for tab navigation. I don't see the iOS version of Vivaldi having any features that would be compelling enough to degrade my user experience by switching to it.
The only other bottom address bar browser with gestures that I have seen is Kiwi on Android and I am surprised this paradigm is still not more common.
Telefunc is another alternative without the boilerplate where on the frontend you can just import and execute the backend functions remotely.
https://telefunc.com/