Is Dark Reader slowing down your browser?

First: confirm it is actually the extension

Browsers get slow for many reasons, and blaming the most recently installed extension is a reliable way to remove the wrong thing. Run this:

1. Open a new window in Incognito mode. Extensions are disabled there by default. Browse normally for a few minutes.
2. If it is still slow, the extension is not your problem — go to Chrome’s Task manager (Shift+Esc) and look at which tab or process is consuming CPU and memory.
3. If Incognito is noticeably faster, re-enable extensions one at a time until it slows again.

Shift+Esc is the underused step here. It shows per-tab and per-extension CPU and memory, so you can see an extension’s cost directly rather than inferring it.

What the numbers actually say

• Speedometer 3.1, filed by users on the project’s tracker: Chrome 49 → 22, Firefox 37 → 15 with the extension active.
• Independent roundups put the category range at roughly 9% slowdown for the lightest extensions up to about 40% for the heaviest.
• Multiple reports describe growth over time — fine for a week or a month, then progressively slower, with the slowdown extending to sites on the exclusion list. Disabling or reinstalling restores speed for a while.

Note that Speedometer measures JavaScript-driven UI work, so it is a harsher test than reading an article. Do not read “49 → 22” as “my browser is half as fast at everything.” Read it as evidence that meaningful work is happening on every interaction.

Why restyling a page costs anything at all

Applying dark mode is not a one-off paint job. To do it well an extension has to:

• Read every stylesheet, including ones loaded from other origins.
• Work out what each colour is — a surface, text, a border, a shadow.
• Compute a replacement colour for each.
• Keep watching the DOM, because pages add and change elements constantly after load.

That last item is the expensive one. A modern web app can fire thousands of DOM mutations while you scroll a feed. An extension that responds to each one individually does an enormous amount of redundant work; one that coalesces them into batches and caches results keyed on the colour and the active theme does far less. Same visible outcome, very different profile — which is why “dark mode extensions are slow” is not a law of physics, it is an implementation choice.

If you want to keep Dark Reader

• Switch mode. Dynamic is the most expensive. Filter or Static are dramatically cheaper, at the cost of worse-looking results and darkened images.
• Exclude your heaviest sites. The web apps you keep open all day — mail, chat, dashboards — usually have their own dark theme anyway.
• Restart the browser more often. Crude, but if your slowdown accumulates it genuinely helps.
• Reinstall periodically. Several users report this clears it, which fits the accumulated-state theory.

If you want to switch

The thing to evaluate is not a marketing claim about speed, it is when the tool does its work. Ask:

• Are the theme styles pre-generated and registered to run at document start, or computed by script on every page load?
• Are colour computations memoised, and is the cache bounded?
• Are DOM mutations coalesced, or handled one at a time?

Eclipse is built around those three answers — pre-generated CSS registered to apply before first paint, a bounded memo cache keyed on colour, role and theme, and a coalescing mutation observer. That design is also what removes the white flash, since both problems come from the same decision about when work happens.

Being straight about it: Eclipse is new, so it has nothing like Dark Reader’s years of real-world coverage. If broad site compatibility matters more to you than speed, that trade-off does not favour us. See the full comparison.

Try it yourself: Eclipse applies a generated dark theme to any site, with per-site overrides and live brightness and contrast controls. Free, no account, no site limits.

Other things that are probably not the extension

• Too many open tabs. Still the leading cause. Check Shift+Esc.
• Hardware acceleration disabled. Settings → System.
• Other extensions. Ad blockers with large filter lists and password managers both do per-page work.
• A stale profile. Testing with a fresh Chrome profile separates profile problems from extension problems.

Product and website names mentioned here belong to their respective owners and are used only to describe what they do. Eclipse is an independent extension and is not affiliated with, endorsed by, or sponsored by any of them.

Related guides

Dark Reader Alternatives: An Honest Comparison
Dark Reader is the category leader and genuinely good. Here is where it struggles — measured, not asserted — and which alternative fits which problem.

Why Dark Mode Flashes White — and How to Stop It
That stab of white between page loads is a race condition, not a bug in your eyes. What causes it, why it is hard to fix, and what a fix requires.

How Dark Mode Extensions Actually Work
CSS filters, stylesheet rewriting, and generated themes are three different machines. Knowing which one you are running explains every quirk you have hit.

Best Dark Mode Chrome Extensions, Compared
Six extensions scored on rendering approach, performance cost, privacy and per-site control — including which ones are filters wearing a theme’s clothing.

Browse all 16 guides →