Sidebar Toggle — sinanm89

Reclaim your screen. Sidebar Toggle hides the space-wasting sidebars and top bars on the sites where they get in the way, so the content you actually came for fills the window.
Supported sites:
• Wikipedia — hide the left navigation sidebar
• old.reddit.com — hide the right sidebar and widen the posts
• YouTube — hide the top bar and the left guide sidebar (just the videos)
• GitHub — hide the global top navigation header
Plus, on YouTube: a "cinema dim" mode that spotlights the player using YouTube's own theater view and blacks out everything around it — great for focused watching. It leaves your theater setting exactly as it found it.
How it works:
• Click the toolbar icon for the popup — toggle the current site, toggle cinema dim, and pick which sites the extension is active on.
• Or use keyboard shortcuts: Ctrl+Shift+E to toggle the current site, Alt+E for YouTube cinema dim. (Firefox may show these as unset until you assign them under about:addons → Manage Extension Shortcuts.)
• Your choices sync across your signed-in browsers.
Private by design: no accounts, no tracking, nothing leaves your browser. Settings live in your browser's sync storage, and the extension can only touch the four supported sites.
Open source (GPL-3.0): https://github.com/sinanm89/Sidebar-Toggle