Cute Chrome extensions that don't slow your browser down

Decorative browser extensions have a reputation, and it is mostly deserved: heavy, chatty, and installed with a permission list nobody read. Which is a shame, because the category is genuinely fun and every one of the problems is avoidable.

Three things worth checking

• The permission list. Chrome shows it before you install. Storage is a preferences file. Tabs, cookies, history and webRequest are the ones that let an extension watch what you browse.
• Whether it touches your page's layout. An extension that inserts elements into the document flow, or measures element positions on every scroll event, can make a smooth page stutter no matter how little it draws.
• Where it sends requests. A decoration with a busy network tab is doing a second job you were not told about.

Why layout is the one that bites

Reading a layout property — an element's height, its position on screen — forces the browser to finish any pending layout work before it can answer. Do that inside a scroll handler and you have asked the browser to stop and measure sixty times a second, on a page it was halfway through drawing.

That is the mechanism behind most “this extension makes scrolling laggy” complaints, and it is invisible until someone profiles it. The fix is unglamorous: never read layout during a scroll, write only transforms, and let the compositor do the moving.

What that looks like here

scrolldog is a small pixel pet that runs along the edge of every page at your scroll speed. It is also a worked example of the checks above, because it had to pass them to be tolerable to live with:

• Two permissions: storage and unlimitedStorage. No tabs, no cookies, no history, no webRequest.
• One host permission — api.scroll.dog — used to check a licence, never to touch the page you are on.
• The pet lives in a fixed, zero-size track and only ever writes a CSS transform, so your page's own layout never changes.
• Scroll is listened to passively and collapsed to one write per animation frame.
• One switch removes it from every open tab instantly.

None of that is a boast — it is the minimum. A thing whose entire job is to be nice to look at has no business making anything slower.