A bit of context, since this is much less serious than it may have sounded:

I use a single browser instance in a tiled window manager, occupying a fixed window directly in front of me, usually with a sidebar open. When a site intentionally centers a fixed-width container, the sidebar leaves that container visibly off the dead center of my screen. I happen to dislike that. This is a personal aesthetic preference for my particular setup, not a claim that viewport centering is generally wrong.

The intended behavior does not remove content or replace responsive layout. The sidebar still narrows the webview and the page reflows normally, the correction only repositions the container that was already meant to be centered, so its center remains in the same physical place. If content ends up covered, offscreen, or stuck in the wrong state, that’s a bug.

I don’t particularly mind the brief movement while toggling a sidebar, since the browsers I use already visibly resize and reflow pages while doing so.

I’m considering reverting the behavior on the blog and keeping it extension only. I’ve also added GIFs to the post showing the intended effect.