I assume you’re talking about the formatting of the posts in this forum, right? What exactly do you want to achieve? The available options are limitted. But Inline code works just as expected, I’d say.
I think subtle is an understatement especially when the dark theme body text background is 0x333131 and the inline code background is 0x333333 ¯\(ツ)/¯. Oh well.
For a bit of fun I found a way to override this and put together a quick script to change the settings. You should close all instances of FireFox before running the script.
It should only update the default FireFox profile and if you already have custom settings it should append these settings, not overwrite the current files. Even so, use it at your own risk.
I’ve used var(--highlight) which is defined in each theme’s color_definitions.scss file and for demo purposes provides a lot of contrast . You can use right-click | Inspect to view the various definitions; alternatively, use the colour name or RGB value.
When I finally managed to re-attach my retina I figured a setting I could live with. Unfortunately the browser I use does not support a UserContent.css stylesheet.