There's the fundamental assumption here that the entry point outhgt to sit atop cruft that publishes the user's content to the world. That may have been meaningful during the utopian days of HTML/CSS on a pre-weaponized internet. Today, it is a bizarre and counterproductive assumption.
Why isn't the entry point <Ctrl-shift-c> into devTools, for example? There you can view, measure, test, and get feedback on anything in the window. Learn a single command or even single url to make the content editable so that you can type, "Hello world" to yourself. Paste an image from somewhere else on the web. Style it, move it around.
Then when you're done, close the window and it goes away, like it should. Because you don't actually know how to publish anything to the world yet. And it's quite possible you don't want or need to do that yet.
This provides a nice self-test because when you next open an about:blank window you have to do everything again from memory to get your content to display.
Who knows, maybe the entire forum will eventually get fed up that Firefox doesn't yet allow you to set svg shape width/height/x/y/etc. through CSS. What a pain, they'll say. And then they'll all threaten to switch to Chrome en masse to force Firefox to implement the most sensible part of SVG2.
The forum may have other priorities in addition to that. :)