Mozilla Thunderbird won’t open in Windows 10 [FULL FIX]

Ivan Jenic
by Ivan Jenic
Troubleshooting Expert
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  • Thunderbird is a great email client, but sometimes it won’t open on a Windows PC.
  • Starting it in Safe Mode or reinstalling are some of the solutions we detail below to help you fix the issue.
  • Learn how to fix more issues related to this email client by reading our articles in the Thunderbird section.
  • Even more useful guides for other email clients can be found in our Email Hub.
thunderbird won't open

Mozilla Thunderbird is one of the most trusted email clients on the market available on various platforms used not only as an email client but also as an RSS feed and much more. And the best part? It’s an open-source project.

However, even though this email client is frequently updated and well-coded, users are experiencing a number of issues with the software.

One is critical and it’s related to sudden crashes after startup. For this purpose, we prepared a simple but useful workaround that should help you resolve it.


What can I do if Mozilla Thunderbird won’t open in Windows?

Although a solid email client, many users reported that Thunderbird won’t open on their PC. This can be an issue. Speaking of Thunderbird, here are some similar issues reported by users:

  • Thunderbird not responding – Many users reported that Thunderbird isn’t responding at all. This can be due to your Thunderbird profile, but you can fix that by deleting parent.lock file.
  • Thunderbird won’t start/ missing profile in Safe Mode – These Thunderbird issues can appear on any version of Windows, but even if you don’t use Windows 10, you should know that most of our solutions can be applied to both Windows 8.1 and 7.
  • Thunderbird won’t start already running – If you’re getting this error message, be sure to open Task Manager and close all Thunderbird instances. After doing that, try to start the application again.
  • Thunderbird won’t launch – Many users reported that Thunderbird won’t launch on their PC at all. This can be a problem, but you can fix it simply by running Thunderbird in Safe Mode.
  • Thunderbird won’t start after crash – Sometimes a crash can damage your Thunderbird profile, and in order to fix that, try reinstalling the application.

1. Delete parent.lock file

  1. Close Mozilla Thunderbird.
  2. Right-click on the Taskbar and open Task Manager.
    Thunderbird won't start Windows 7
  3. Under Processes, find and kill all Thunderbird-related processes.
  4. Now, press Windows key + R to bring up the Run command.
  5. Type %appdata% in the command line and press Enter.
    Thunderbird won't start already running
  6. Open the Thunderbird profile folder.
  7. Find and delete the parent.lock file. You may need administrative permission to do so.
  8. Start Thunderbird again. It should now function without any problems.

These steps should also correct any issues with your Thunderbird user profile, in case it is corrupted.


Thunderbird is slow on Windows 10? Speed it up with these easy solutions


2. Consider switching to a different email clientThunderbird not responding

If the previous solution didn’t fix the problem with Thunderbird, this might be a good time for you to consider switching to a different email client.

There are many great email clients available, but if you want one that is similar to Thunderbird, we recommend you try out eM Client (free download).

Due to its seamless integration with other email clients like Gmail, Exchange, and Outlook, eM Client is one of the best software options on the market.

You can easily transfer complicated schedules from your calendar, and also add contacts from other third-party software, allowing you not to worry about your data not being compatible.

Some of the most important features of eM Client include:

  • Integrated chat app compatible with any other chat service
  • Automatically translate emails
  • Set up delayed times for sending your emails
  • PGP encryption that offers you a secure environment
eM Client

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3. Reinstall Thunderbirdreinstall thunderbird

According to users, sometimes Thunderbird won’t open if your installation is damaged. This can be a big problem, but one of the easiest ways to fix the issue is to reinstall Thunderbird. There are several ways to do that, and you can do it right from the Settings app.

It’s worth mentioning that Thunderbird, like many other applications, can sometimes leave certain files and registry entries, even after you uninstall it. This can be a problem, and it might cause the issue to reappear once you install the application again. To remove these files, we recommend using a third-party app, Revo Uninstaller.

With Revo, you also make sure that the multiple files, folders, and/or Registry entries of the respective program are not left on your system, in which case they can cause various issues.

After installation, Revo is extremely intuitive to use: you can see all installed applications on your PC in one single pane. For there, you can easily search for the desired program using the search bar at the top and choose to remove it.

With the free version of the tool, you can scan for program leftovers and remove them, uninstall Windows apps or browser extensions. Furthermore, with the paid version you can also use the Forced Uninstall or Quick/Multiple Uninstall options.

Once you remove Thunderbird using this application, install it again, and check if the problem is resolved.

Revo Uninstaller

Revo Uninstaller

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4. Start Windows in Safe Mode

  1. Press Windows Key + I to open the Settings app.
  2. Go to Update & Security section.
    Thunderbird won't launch
  3. In the left pane, select Recovery. In the right pane, click Restart now in Advanced startup section.
    Thunderbird won't start after crash
  4. Now select Troubleshoot > Advanced options > Startup Settings > Restart.
  5. Once your PC restarts you’ll be presented with a list of options. Press F5 or 5 to select Safe Mode with Networking.

Once you start Windows in Safe Mode, try to run Thunderbird again. If the issue is still there, start Thunderbird in Safe Mode and check if that helps.


5. Start Thunderbird in Safe Mode

  1. Press Windows + R to bring up the Run command.
  2. Type thunderbird -safe-mode and press Enter.
    Thunderbird won't start already running

If you want a more user-friendly way to start Thunderbird in Safe Mode, simply locate Thunderbird shortcut, press and hold the Shift key and start the application.

After doing that, a new window will appear. Just click Continue in Safe Mode to start the Thunderbird. If the issue doesn’t appear, it means that your add-ons or toolbars are causing the issue.

To permanently fix the problem, repeat the process again, but this time check Disable all add-ons and Reset toolbars and controls. Now click Make Changes and Restart button.

This is useful if the issue is caused by your configuration or third-party add-ons. Thunderbird supports a wide array of add-ons allowing you to enhance its functionality, but sometimes certain add-ons can interfere with your system and prevent you from starting Thunderbird.


6. Restart and reset your modem

Thunderbird not responding

Several users reported that they fixed the issue with Thunderbird simply by restarting their modem. This is rather simple, and in order to do it, you just need to press the Power button on your modem, wait for a few seconds and then turn it back on again.

Once your modem restarts, check if the problem is still there. If the issue persists, you need to reset your modem. To do that, you just need to press and hold the hidden Reset button for a couple of seconds. For more information on how to reset your modem, we suggest that you check its instruction manual.

If the issue is resolved after resetting your modem, keep in mind that you might have to set up your wireless connection and other settings again.


7. Try using the portable version

If Mozilla Thunderbird won’t open on your PC at all, the issue might be related to its installation. As a workaround, users are suggesting to download and run the portable version of Thunderbird.

This version doesn’t require installation, and it won’t add any information to the registry, so it won’t be affected in any way by the previous Thunderbird installation.

Once you download the portable version, run it and check if that solves your problem. If the issue doesn’t appear, you might have to switch to the Portable version until you fix the problem.

Hopefully, your email client is put and running by now. However, if you have any remarks or questions regarding the subject, use the comments section below!


FAQ: Learn more about Thunderbird

  • Why is my Mozilla Thunderbird not working?

Users reported many instances when Thunderbird was unresponsive. There are multiple causes, from interfering add-ons to missing updates.

  • Is Thunderbird email still supported?

Yes, it is still supported. Actually, Mozilla is now launching updates for it more frequently now.

  • Is Thunderbird better than Gmail?

Each email client has its own pros, and both Thunderbird and Gmail are considerably popular. To convince yourself, you could try them both since downloading is free.

Editor’s Note: This post was originally published in April 2017 and was completely revamped and updated in July 2020 for freshness, accuracy, and comprehensiveness.


Editor's Note: This article was originally published in April 2017 and was revamped and updated in July 2020 for freshness, accuracy, and comprehensiveness.