How to Fix Firefox High CPU Usage on Linux

What Causes This?

Firefox high CPU usage on Linux usually happens when too many tabs, extensions, or background web scripts are competing for system resources. Hardware acceleration problems, a bloated browser cache, or a damaged Firefox profile can also make the browser work much harder than it should. In some cases, another app running in the background adds extra load, making Firefox look like the main problem even when the whole system is under pressure.

Common Symptoms

• Firefox makes your system feel slow or laggy
• One or more firefox processes stay near the top of CPU usage monitors
• Fans spin up loudly while browsing simple websites
• Video playback stutters or pages become slow to scroll
• CPU usage drops as soon as Firefox is closed

How to Fix It Manually

1. Check whether Firefox is really using the CPU

   1. Open a terminal.
   2. Run:

      top

      or:

      htop

   3. Look for firefox or Web Content processes using a high percentage of CPU.
   4. If usage spikes only on one site, that tab is likely the cause.

2. Find and close the problem tab or process

   1. In Firefox, press Shift+Esc to open Firefox Task Manager.
   2. Sort by CPU usage.
   3. Identify the tab, extension, or subframe using the most resources.
   4. Close that tab, reload it, or end the process from Firefox Task Manager.

3. Disable unnecessary extensions

   1. In Firefox, press Ctrl+Shift+A to open Add-ons and Themes.
   2. Click Extensions.
   3. Disable any extension you do not need, especially ad blockers, shopping tools, VPN add-ons, or tab managers running all the time.
   4. Restart Firefox and check CPU usage again.

4. Clear Firefox cache

   1. Open Firefox menu > Settings.
   2. Go to Privacy & Security.
   3. Scroll to Cookies and Site Data.
   4. Click Clear Data.
   5. Select Cached Web Content, then click Clear.
   6. Restart Firefox.

5. Turn hardware acceleration off or on

   1. In Settings, scroll to Performance.
   2. Uncheck Use recommended performance settings.
   3. Toggle Use hardware acceleration when available off.
   4. Restart Firefox and test.
   5. If CPU usage gets worse, turn it back on. Some Linux graphics drivers behave better one way than the other.

6. Test Firefox in Troubleshoot Mode

   1. Click the Firefox menu > Help > Troubleshoot Mode.
   2. Confirm the restart.
   3. Browse normally for a few minutes.
   4. If CPU usage improves, the issue is likely caused by an extension, theme, or custom setting.

7. Refresh your Firefox profile if the problem continues

   1. Type about:support in the address bar and press Enter.
   2. Click Refresh Firefox.
   3. Confirm the reset.
   4. This keeps important data like bookmarks and passwords, but removes problematic customizations and add-ons that may be driving CPU usage.

Fix It Automatically with Kudu

If you do not want to hunt through tabs, extensions, cache files, and background clutter manually, Kudu can help automate the cleanup. It can identify resource-heavy junk, reduce unnecessary background load, and make it easier to fix the conditions that often lead to high Firefox CPU usage.

Download Kudu Free →