Not a user of ‘autohide_sidebar.css’… however on testing (new profile of Fx132.0.2 on Win10) it appears that the behaviour of the userstyle has changed after a recent Firefox update and/or a recent Commit? Was this change intended or not?

IIRC the userstyle’s previous behaviour when the sidebar opened on hover, was that the page Content window was resized smaller to accommodate the presence of the expanded sidebar? Thus no page content was obscured.

Using the current version of ‘autohide_sidebar.css’ the open sidebar now overlays and obscures part of the page Content window.

See recent r/FirefoxCSS topic ‘Sideberry Autohide Doesn’t Work’.