This is what the right-click menu looks like in Firefox on macOS [1]. Compared to the right-click menu from Safari on the same machine [2], you can see several differences. The most notable one is that the Firefox menu is not theme-aware, rendering a light-themed context menu even though the OS is in dark mode. Next, the padding around the menu is incorrect compared to a native menu. It also looks like the font is maybe a different size. Finally, the drill-down arrow on the Firefox menu doesn't match the native one.
I also want to add that the behavior is different: holding the right mouse button then releasing closes the native context menu, but doesn't close the Firefox context menu. Going into "mission control" closes the native context menu, but not the Firefox context menu. There are a few other differences as well.
99% of the time I use "Look Up" which is the top item in native macOS context menus (for selected text). It's really annoying when your browser is missing it.
This is likely a separate ticket, but Firefox ignores macOS' built-in text replace which I use for expanding text like my email address.
