Firefox Is Slow or Using Too Much Memory? Free Up RAM and CPU

Published ✓ Verified ⏱️ 2 min read July 14, 2025 · by Ryan Bennett

Firefox feels sluggish, fans spin up, or it shows gigabytes of RAM in Windows Task Manager.

Why: A single heavy tab (web mail, a video call, a maps page) or a leaky extension is usually doing the damage, and Firefox left open for days slowly accumulates memory. Less often, hardware acceleration is off, so the CPU is doing work your GPU should handle. Find the culprit first, then tune.

Fix 1: Find the heavy tab or extension

Type about:processes in the address bar and press Enter to open Firefox’s own Task Manager.
Sort by Memory or CPU and look for the worst offender. Close that tab, or click the arrow to expand it and end a single runaway subframe.
Extensions appear here too. If one is high, go to about:addons and disable it.

To rule out add-ons in one move, restart in Troubleshoot Mode: menu (≡) → Help → Troubleshoot Mode… → Restart. This launches with all extensions and themes off. If Firefox is suddenly fast, an add-on was the cause.

Fix 2: Turn hardware acceleration on, then restart

Open menu (≡) → Settings → General and scroll to Performance.
Untick Use recommended performance settings, then tick Use hardware acceleration when available.
Restart Firefox. Offloading rendering to the GPU cuts CPU and memory use on most machines.

Firefox also accumulates memory the longer it stays open, so a periodic full restart (close every window) reclaims it. To free RAM immediately without restarting, open about:memory and click Minimize memory usage.

Fix 3: Update, then Refresh as a last resort

Update first: menu (≡) → Help → About Firefox downloads any update; click to relaunch. Each release ships performance fixes.
If it is still slow with no obvious heavy tab, Refresh Firefox restores default settings while keeping your bookmarks, passwords and history: menu (≡) → Help → More troubleshooting information → Refresh Firefox….

FAQ

Is 2-4 GB of RAM normal for Firefox? Yes, with many tabs and extensions. Modern Firefox spreads tabs across multiple processes for stability, which trades some RAM for fewer crashes. It only matters if your PC is short on memory — close tabs and check about:processes.

One tab pins my CPU at 100%. That page’s scripts are the cause (common with web mail and dashboards). Close it, or disable extensions that inject into it via Troubleshoot Mode (Fix 1).

Sources: Mozilla Support — Fix Firefox using too much memory or CPU resources