I'm using firefox on macos right now and I can't see what the issue is. The the menus show up in the main top bar like every other app. Am I missing something?
I just checked again and the firefox one looks so close to the native right click that I can hardly tell the difference other than it not supporting dark mode
Firefox's engineers have done a remarkable job at trying to mimic the native context menu as much as possible, but it's not a 100% match (as evidenced by your discovery that it doesn't support dark mode). There have also been times over the past two decades where macOS updated something about the context menu that then make the Firefox one not match. The main point is that it really should just be a native menu; they shouldn't be spending time trying to make it match 100%.
I know of a lot of people like that, when presented with very illogical UI decisions, or controls that look absolutely nothing like the rest of the system, they just cannot see what the issue is. I wonder if it’s poor eyesight, lack of attention, or whatever.
I suspect it’s that they don’t care. It’s not an issue for them because they don’t use the missing native functionality anyway.
Also, if you frequently use cross platform software on multiple platforms, it’s possible consistency within the app is more important than consistently with the OS.
People that come from a Linux desktop background seem to be immune to these things. The rough sandpaper that is open source UI will eventually wear anyone’s awareness down.