How to fix common Firefox issues on Mac

Mozilla's Firefox browser is known for its speed and a large collection of extensions that let you customize the experience to your heart's desire. But when Firefox is running slow, crashing, or not loading websites properly, it can be frustrating to figure out why. Follow my step-by-step guide to get your Firefox back to tip-top condition. All instructions are updated for macOS Tahoe and later and Firefox 150.0+.

Or get CleanMyMac standalone via Marketplace — no membership needed.

Most common Firefox problems

Overall, Firefox is a top-rated and highly reliable browser. It's a good choice for both professional and everyday users. However, with so many platforms, devices, and screens to serve, even the best can sometimes fall short. In this how-to, I've combined the most frequently occurring Firefox problems and written specific instructions on how to fix them next:

• Firefox runs slowly, hangs, or keeps freezing
• Firefox crashes unexpectedly or won't open
• Firefox shows errors when loading websites
• Firefox is behaving incorrectly (e.g., extensions not working, settings not saving)

Let's tackle each of these, step by step, with the troubleshooting table:

Common Firefox issue	Quick fix
Firefox is slow or freezes	Close tabs, clear cache, update Firefox; use CleanMyMac to clear browser data in one scan.
High hardware usage dragging browser	Check Activity Monitor; Use iStat Menus — live CPU/RAM stats in menu bar.
Firefox crashes or won't open	Restart in Troubleshoot Mode, reinstall; Use Moonlock to remove malware causing crashes.
Websites won't load	Check network, flush DNS, reset proxy; Use WiFi Explorer to diagnose signal and interference
Extensions / settings broken	Refresh Firefox or create a new profile
Ads slowing down page loading	Use a content blocker in Firefox, or use AdLock to block ads and trackers system-wide

Want to go further than the fixes in this guide? The Productivity Tools GPT assistant can help you identify which apps and habits are taxing your Mac — the same root causes that drag Firefox down.

Why is Firefox slow, hanging, or freezing?

Most slowdowns happen because Firefox is hogging RAM — too many open tabs, outdated code, or a rogue extension can quickly exhaust your Mac’s resources. A slow Firefox browsing experience is, truthfully, beyond annoying. It seems like it's almost working, but you can't get anything done. 

Here I've listed some suggestions that should get your Firefox running faster again.

1. Close inactive tabs

See how many tabs you have opened. More than a few? Active tabs mean active processes that consume your laptop's RAM and drastically reduce its performance. Just close the tabs you're not actively using. If they're important to remember, bookmark them or add them to your task manager — 2Do is good for this if you're already using it for work tasks.

I use 2Do for batch scheduling tasks, including closing inactive tabs, since they tend to pile up quickly. Plus, it’s a great tool to break down big tasks into smaller ones. For example, you can set a “Firefox cleanup” task and break it down into subtasks, like cache cleaning, updates, etc. The subtask feature lets you make tiny changes that lead to major transformations, just like in James Clear's Atomic Habits.

2. Clear Firefox cookies and cache

All the websites you visit leave behind cached image files, which are meant to speed up load times, and cookies, which can save you from having to log in repeatedly. These features are really handy when they work properly, but sometimes cache and cookies can cause glitches and slowdowns.

If Firefox is acting up, you can clear cookies and cache by doing the following:

1. Open Firefox, then click Firefox in the menu bar > Settings (or Preferences for older macOS).
2. Click Privacy & Security > Cookies and Site Data.
3. Click Manage browsing data > Click Remove All Shown.

Tip: In case you want to delete cookies for a certain website, choose it from the list or type in the search field > Select > Click Remove selected.

Source: support.mozilla.org

If you want to do a thorough cleanup of Firefox, check out the quick guide on how to delete incognito history on Mac.

3. Update Firefox and macOS

If closing tabs and clearing the cache didn't work, it's a good idea to update macOS and Firefox to their latest versions. 

Here’s how to update both:

• macOS update: Go to System Settings > General > Software Update. Install any available updates.
• Firefox update: Click on Firefox in the menu bar > About Firefox. The latest available update should start downloading automatically. When it's ready, click Restart to Update Firefox. 

4. See what consumes hardware resources

Overloaded hardware resources are a common cause of Firefox slowdowns. For basic information, you can use Mac's native Activity Monitor, but it looks like a spreadsheet, and you need the time to load and understand what’s hogging your Mac. 

A better solution to monitor your Mac is to use a pro-level app, such as iStat Menus. The app lives in your menu bar and shows stats for CPU, GPU, RAM, and more, with percentages (you decide what stats to show). When you open it, you’ll immediately see how your Mac is overloaded and which hardware resource is being used the most, so you can take action right away. 

Firefox overloading your Mac? iStat Menus shows you exactly what's happening. Live CPU, RAM, GPU, and network stats in your menu bar — see which process is killing performance before Firefox even tells you. Try iStat Menus Free.

5. Troubleshoot plug-ins and extensions

When Firefox stops responding to your clicks, it's very likely that one of your installed plug-ins is the culprit. 

To check for that:

1. Go to Menu > Add-ons and themes > Extensions.
2. Disable all extensions, then re-enable them one by one to find the problematic one.
3. For plug-ins, type about:plugins in the address bar. To disable, follow Mozilla’s instructions.
4. Remove unwanted extensions directly in Firefox.

Updated Firefox means better security and speed. Use the guide on updating Firefox for Mac to prevent issues.

6. Stop loading resource-heavy content

Some websites use heavy video or ad content that can eat up system resources, especially if you keep many tabs open. Luckily, you can stop loading it by default until you ask for it.

Consider using a privacy extension from Mozilla’s add-on site to minimize unnecessary content. 

Or use an ad blocker —AdLock blocks ads, pop-ups, and trackers system-wide across all browsers. In the Settings tab, you can find filters such as Social Media, Counters, and analytics.

The tips above cover the most common Firefox issues on Mac. But if you're still experiencing troubles, there is more you can do. 

Read also:

• Fix Safari Problems on Mac
• Fix Chrome Problems on Mac
• Fix Dns Failure Error on Mac
• Enable Cookies on iPhone

Firefox crashes unexpectedly or won't open

Start by restarting your Mac, and then clear the cache and troubleshoot your plug-ins as described above. If the browser still quits or refuses to launch, try a clean reinstall (it usually does the trick).

How to reinstall Firefox safely

Whether Firefox crashes on startup or in the middle of browsing, I've found that reinstalling the application usually does the trick.

1. Quit Firefox if it's running.
2. Open your Applications folder and move Firefox to the Trash.
3. Download the latest version from the official Mozilla website.
4. Drag the new Firefox app into your Applications folder.

Firefox shows errors when loading websites

When a page won’t load, the culprit is usually one of three things: an unstable connection, stale website data, or security software blocking the request.

Your Firefox runs fast and doesn’t randomly quit, but it still fails to load websites. Here’s how to troubleshoot:

1. Check your network connection

Try turning your modem off and back on – this simple step has resolved most connection issues in my experience.

Also, you can test your connection with a browser like Safari or Chrome. If the network is the issue here, use WiFi Explorer, a Wi-Fi analyzer, to check your signal. And don’t worry, you don’t need to be a proficient system admin to see what’s wrong with the network and how to troubleshoot it. 

If you also have a range of Wi-Fis available, the app can show you the signal strength, so you can pick the faster one. For heavy network workloads, I usually connect to Wi-Fis with at least 70% signal strength. 

2. Launch websites in other browsers

If your Wi-Fi network seems to be fine, it's good to check whether the connection works in other browsers, like Safari or Chrome, just to make sure that the problem, in fact, is with Firefox specifically. Then, check the settings in your firewall by following the steps outlined by Mozilla.

3. Fix the proxy server issue

If, upon loading the website, you get the "Proxy server is refusing connections" message, there is an easy fix for that:

1. Go to Firefox > Settings > General > Network Settings.
2. Click Settings.
3. Select No proxy.
4. Click OK and restart Firefox.

4. Validate the security certificate

In case Firefox shows you that it has trouble validating some website's security certificate, it might be related to an improperly set date and time on your system.

If Firefox warns about a site's security certificate:

• Check your Mac’s date and time in System Settings > General > Date & Time.
• Set the correct time zone and restart Firefox.

5. Flush DNS cache

Another option you can try is flushing the DNS cache, which acts as a temporary database, storing all sorts of connectivity logs and website access attempts.

1. Open Terminal (Applications > Utilities).
2. Type:

sudo killall -HUP mDNSResponder; say DNS cache has been flushed

3. Press Return and type your admin password when prompted.

4. An alert a few moments later will inform you that the process is complete.

Combine flushing the DNS cache with clearing out cache and cookies from Firefox, and restarting your Mac to get the best result.

6. Disable DNS prefetching

Usually, Firefox tries to speed up loading new websites by using DNS prefetching, but it can also cause loading errors with some system configurations. 

To disable DNS prefetching:

1. In the address bar, type about:config and press Return. 
2. The about:config "This might void your warranty!" warning page may appear. Click I accept the risk! to continue.
3. Hold down the Control key while you click on the list of preferences. Select New and then select Boolean.
4. In the Enter the preference name field, type network.dns.disablePrefetch and click OK.
5. Select True when prompted to set the value and click OK.

7. Scan your Mac for malware

Ad pop-ups, unfamiliar toolbars, or a changed homepage are signs of malware hijacking Firefox.

For ongoing malware protection, Moonlock runs in the background and monitors your Mac in real time.

8. Make sure security software isn’t blocking Firefox

Occasionally, a macOS security update causes Firefox to lose trusted app status. This happens when your Mac's firewall used to recognize previous versions of Firefox but no longer trusts the new one.

To fix it:

• Check your firewall settings in System Settings > Network > Firewall.
• Add Firefox to your allowed apps list if needed.

Read also:

• How to safely clear cache on Mac
• How to clear browsing history on Mac
• How to make Internet downloads faster

Firefox still not working correctly

If Firefox is still misbehaving—extensions not working, settings not saving, or other odd issues—try these advanced fixes.

1. Restart Firefox in Troubleshoot Mode (formerly safe mode)

When clearing the cached data doesn't help, try restarting the browser in safe mode. This will temporarily turn off your extensions, as well as any extra themes and toolbars, and hardware acceleration. 

To do this:

1. Quit Firefox.
2. Hold down the Option key and open Firefox. Or, type about:support in the address bar and click Restart with Add-ons Disabled.

If the problem goes away in safe mode, you can check your extensions, themes, and anything else you've added to Firefox.

2. Refresh Firefox

The Refresh Firefox feature resets settings and removes extensions and themes, but keeps your bookmarks, history, passwords, and cookies.

To refresh it:

1. Open Firefox, and type about:support in the URL bar, which takes you to the Troubleshooting Information page.
2. You'll find a lot of information about your browser installation, as well as the Refresh Firefox button at the top-right.
3. Click Refresh Firefox.

3. Create a new Firefox profile

If neither option fixed the problem, try creating a fresh Firefox profile, which won't have any of your bookmarks, passwords, and user preferences, but might get rid of the problem.

1. Open the Terminal (Applications > Utilities).
2. Type in /Applications/Firefox.app/Contents/MacOS/firefox-bin -P.
3. Press Return, and the Profile Manager window should open.
4. Click Create Profile… then Next and enter the name for the profile.
5. Click Done

4. Turn off hardware acceleration

In cases when safe mode seemed to fix the problem but checking plug-ins didn't bring any result, the problem may hide in hardware acceleration, which is off by default in safe mode. Here's how to turn it off in the regular mode, too:

1. Go to Firefox > Settings > General > Performance.
2. Deselect Use recommended performance settings and Use hardware acceleration when available.
3. Restart Firefox.

Firefox not working on Mac? You have the fixes

About a dozen apparent and not-so-apparent tips should bring your Firefox to the best shape possible. And even if you don't experience many troubles with Firefox, following some of the tips above would help you optimize its speed and responsiveness.

Along with the native fixes, I also recommend using: 

• CleanMyMac to clear your browser cache and history, as well as your Mac, and remove any malware instantly.
• AdLock to block ads and pop-ups that slow down your browser.
• iStat Menus to monitor your Mac's performance and take action (an overloaded Mac can cause Firefox glitches and slowdowns).
• WiFi Explorer to monitor and troubleshoot network issues.

A slow, crashing Firefox is a Mac problem as much as a browser problem. CleanMyMac, iStat Menus, AdLock, and WiFi Explorer — all on Setapp — target the root causes: browser junk, overloaded hardware, ads, and unstable connections. Get 250+ Apps on Setapp. Or try CleanMyMac first — free for 7 days.