Fix Slow Browser Performance for Web Apps (Run the JavaScript Speed Test)

Confirm the problem with a quick benchmark

Before you change settings, baseline your device so you can tell what actually helped. Open the JavaScript Speed Test and let it finish (don’t switch tabs while it runs). You’ll get a score that’s a quick proxy for “main thread” responsiveness—the part of the browser that runs most UI and app code.

In this guide, you’ll do three things:

• Measure slowness with the JavaScript Speed Test
• Remove the most common causes (throttling, extensions, GPU fallback)
• Re-run the test to verify the fix

Quick answer (do these first)

If you need a fast win, do this sequence in order:

1. Plug in your device and set power mode to Best performance / Performance
2. Close heavy tabs (video, dashboards) and re-run the JavaScript Speed Test
3. Test with extensions disabled (Incognito/InPrivate or a fresh profile)
4. Confirm you’re not in a GPU fallback path with the WebGL Test

If your score jumps and apps feel snappier, you’ve found the bottleneck.

Fix 1: Remove CPU throttling (the #1 “mystery slowness” cause)

Browsers get slow when the CPU can’t boost. This happens on battery, in power saver modes, or when a laptop is running hot.

• Windows 10/11: Settings > System > Power & battery → set Power mode to Best performance (or disable battery saver while testing).
• macOS: keep the laptop plugged in while testing, close heavy background apps, and avoid running the benchmark right after waking from sleep.
• Chromebooks: close unused tabs and restart the browser (ChromeOS can keep background tabs active longer than you expect).

Verification loop: re-run the JavaScript Speed Test right after changing power mode. If your score improves and input delay drops in your web app, throttling was the cause.

Fix 2: Stop extensions from hooking every page

Extensions can add latency by injecting scripts, blocking requests, or scanning page content. This is especially noticeable in large apps (Figma, Notion, admin dashboards).

1. Run the JavaScript Speed Test once in your normal session.
2. Open an Incognito/InPrivate window (with extensions disabled), then run the test again.
3. If the “fresh” run is faster, re-enable extensions one by one until you find the slow one.

Common culprits:

• Ad blockers in advanced modes and script blockers
• Privacy suites that modify headers or storage
• “Tab suspender” tools that constantly manage memory
• Video downloaders, screen recorders, and DOM inspectors

If the slow extension is required for work, keep it installed but add allowlists for your critical web apps (so it does less work on those sites).

Fix 3: Make sure the browser isn’t outdated or stuck in a bad state

You don’t need a reinstall most of the time, but you do need a full restart and an up-to-date build.

• Chrome / Edge: Menu > Help > About → apply updates → Relaunch
• Firefox: Menu > Help > About Firefox → update → restart
• After updating, reboot the device (this clears stale GPU and audio/video processes that can drag performance down).

If the browser has been open for days with hundreds of tabs, a restart alone can restore responsiveness.

Fix 4: Confirm you’re not in a GPU fallback path (WebGL + acceleration)

Many “slow browser” complaints are actually a GPU acceleration problem: the CPU ends up doing work your GPU should handle (rendering, compositing, 3D canvases, heavy animations).

1. Open the WebGL Test.
2. If it fails, or if it shows software rendering, fix GPU acceleration first (it affects many modern web apps).

Chrome / Edge hardware acceleration check:

1. Go to Settings > System and performance
2. Turn on Use hardware acceleration when available
3. Click Restart

If acceleration is already on but WebGL still fails, update your GPU driver (Windows) or apply OS updates (macOS). Then re-run both the WebGL Test and the JavaScript Speed Test.

Fix 5: Reduce memory pressure (tab hoarding feels like “lag”)

When memory is tight, the browser constantly discards and reloads tabs, pauses scripts, and stutters during typing or scrolling.

• Close video-heavy tabs and any “always-on” dashboards.
• Pause background apps that compete for RAM (chat apps, sync clients, IDEs).
• If you’re on an 8 GB machine, avoid running multiple heavy web apps at once (for example: Meet + Figma + a dashboard).

Tip: If a single site is slow but everything else is fine, clear data for that site (not your whole browser):

• Chrome/Edge: open site settings for the domain and remove the site’s stored data, then sign in again.

Fix 6: Reset “experimental” settings that can hurt stability

If you’ve toggled browser flags for testing, you can accidentally force unstable rendering paths.

• Chrome: visit chrome://flags → Reset all → Relaunch
• Edge: visit edge://flags → Reset all → Relaunch

Then re-run the JavaScript Speed Test. If you see fewer spikes and better consistency, a flag was the cause.

Fix 7: Managed devices and enterprise policy limits

On work devices, IT may enforce extensions, disable acceleration, or restrict storage. If the slowness happens only on a managed profile:

• Check chrome://policy or edge://policy for forced extensions or performance-impacting settings.
• Share a screenshot of your JavaScript Speed Test score and (if relevant) your WebGL Test result with IT so they can target the right policy.

Verify the fix (don’t skip this)

Go back to the JavaScript Speed Test and run it twice. You’re looking for:

• A higher score than your original baseline
• Less variation between runs
• Noticeably lower input delay in your actual web app (typing, dragging, scrolling)

If your score improves but one specific app is still slow, the issue is likely app-side (large documents, heavy plugins, a sync backlog) rather than your browser.