Full Fix: Mozilla Thunderbird won’t open in Windows 10, 8,1, 7

Ivan Jenic
by Ivan Jenic
Troubleshooting Expert
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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 of those issues is critical and is related to sudden crashes after the start up. For that purpose, we prepared a simple but useful workaround that should help you resolve it.

How to resolve the ‘Mozilla Thunderbird won’t open’ issue in Windows

Thunderbird is a solid email client, but many users reported that Thunderbird won’t open on their PC. This can be an issue, and 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, Windows 7, 10, 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.

Solution 1 – Delete parent.lock file

According to users, sometimes your Thunderbird user profile can get corrupted, and that can lead to this problem. The simplest way to address this issue is by deleting the ‘parent.lock‘ file found in the profile directory. You can do that by following these instructions:

  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.

Solution 2 – Start Thunderbird in Safe Mode

If Mozilla Thunderbird won’t open on your PC, the issue might be your configuration or third-party addons. 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.

However, you might be able to solve this problem by starting Thunderbird in Safe Mode. Just like Windows, Thunderbird has its own Safe Mode that allows you to run the application with default settings and add-ons. To start Thunderbird in Safe Mode, you need to do the following:

  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.

After doing that, Thunderbird will be reset to default and the issue will hopefully be permanently resolved.

 Solution 3 – Reinstall 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, delete the content of the following directories:

  • Program FilesMozilla Thunderbird
  • WindowsTemp

To completely remove Thunderbird, it’s advised to manually find and delete these files and registry entries. However, this can be a tedious task, even for advanced users, so it might be better to use an uninstaller software.

In case you’re not familiar, uninstaller software can remove the selected application along with all of its files and registry entries automatically, ensuring that the application is completely removed. If you’re looking for a good and simple uninstaller, we recommend you try Revo Uninstaller.

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

Solution 4 – Start Windows in Safe Mode

According to users, Thunderbird won’t open if a third-party application is interfering with it. To check if third-party apps are the problem, it’s advised to start Windows in Safe Mode and try to start Thunderbird again.

To start Windows in Safe Mode, you just have to do the following:

  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.

Solution 5 – 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.

Solution 6 – 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.

Solution 7 – Consider switching to a different email client

Thunderbird not responding

If the previous solutions 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).

The application has a simple and familiar interface, and if you want to learn more about it, we did a review of eM Client, so be sure to check it out for more information.

If you don’t feel like switching to a different email client, you can always use the webmail version to access your emails.

If you have any remarks or questions regarding the subject, use the comments section below!

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