The Hidden Performance Cost of New Tab Extensions You install a new tab extension to make your browser nicer. You get weather, a clock, a background image. But then you notice Firefox feels... slower. The new tab hesitates before loading. Your CPU spikes for half a second. Here's what's probably happening — and how the good extensions avoid it. Problem 1: Synchronous localStorage Access on Startup Every new tab load starts fresh. Your extension needs to load settings. The naive approach: // Slow: synchronous, blocks rendering const settings = JSON . parse ( localStorage . getItem ( ' settings ' )); applyTheme ( settings . theme ); renderClock ( settings . timezone ); Enter fullscreen mode Exit fullscreen mode This is synchronous, which means the browser can't paint anything until localStorage.getItem returns. On slower storage, this adds measurable lag. The fix: // Async: browser can start painting while we load settings async function init () { const settings = await loadSettings (); applyTheme ( settings .…