Standard web browser problems are mostly network-related. Sometimes, though, you’ll be faced with less common issues, such as the “Source file could not be read” error message in Firefox. While the error occurs in other web browsers as well, it seems to affect Mozilla’s product particularly often.

The message shows up in different scenarios but mainly when you try to download a file. The full error message usually reads as follows:

“FileX could not be saved because the source file could not be read.”

FileX represents the path to the file that you could not save, which will be displayed in the error message.

In this article, we’ll show you how to fix the “Source file could not be read” error when downloading a file via the Firefox browser. The solutions in this article have worked for many users.

What causes the problem?

Finding out how to remove the ‘File could not be saved because the source file could not be read’ error message from Firefox for Windows 10 involves knowing the underlying cause of the problem.

Your internet connection is always the prime suspect, and yes, many users found that they weren’t correctly hooked up. Other, less likely causes are as follows:

  • A problematic compreg.dat file
  • A misconfigured network.http.accept-encoding setting
  • Faulty browser extensions
  • A broken Places.sqlite file

Now it’s time to resolve the underlying causes of the error message.

Delete the comprag.dat file

The comprag.dat file is related to many Mozilla Firefox processes. It’s automatically created whenever you download or install any Firefox product, such as Thunderbird. If the file becomes corrupt, it will cause different kinds of problems, the “File could not be saved” error being one of them.

You’ll have to delete the file to resolve the problem. Once the file is deleted, a new one will be created.

Follow these steps:

  1. Launch Mozilla Firefox.
  2. Once the browser comes up, go to the address bar, type “about:support,” and hit the Enter button.
  3. Once the Troubleshooting Information page shows up, go to Application Basics and click on Open Folder beside Profile Folder.
  4. Once the folder opens, search for the “compreg.dat” file and delete it.
  5. Restart the browser and try downloading the file.

Adjust the “network.http.accept-encoding” setting

The network.http.accept-encoding setting helps tell a server what encoding an HTTP client supports. The setting could be the cause of the error message if it’s misconfigured. Follow these steps to adjust it and see if that will resolve the problem:

  1. Open Mozilla Firefox.
  2. Go to the address bar, type “about:config,” and then hit the Enter key.
  3. Once the “Proceed with caution” warning message appears, click on the “Accept risk and continue” button.
  4. Now go to the search box and type “enco.”
  5. Navigate to the “network.http.accept-encoding” setting and double-click it.
  6. Now delete everything in the box and restart the browser.
  7. You can now check if the error persists.

Make sure the places.sqlite file is not set to Read-only

The places.sqlite file is where Firefox saves your bookmarks and keeps a record of your downloaded files. The download error could be showing up because the file is set to Read-only and the browser can’t write new information to it. Turning off the Read-only function will get rid of the problem.

Follow these steps:

  1. Open a File Explorer window by right-clicking the Start button and selecting File Explorer or pressing the Windows and E keys together.
  2. After the File Explorer window opens, navigate to C:\Users\your_user_name\AppData\Roaming\Mozilla\Firefox\Profiles.

C represents your Windows volume, and “your_user_name” is your current user account’s folder.

Alternatively, you can open the folder by following these steps:

  • Launch Mozilla Firefox.
  • Once the browser comes up, go to the address bar, type “about:support” and hit the Enter button.
  • Once the Troubleshooting Information page shows up, go to Application Basics and click on Open Folder beside Profile Folder.
  1. Once the folder opens, search for the “Places.sqlite” file.
  2. After you find the file, right-click it and select Properties from the context menu.
  3. Once the Properties dialog window opens, confirm that the Read-Only checkbox isn’t marked.
  4. If the box is marked, untick it and click on the OK button.

Open Firefox in Safe Mode

Problematic browser add-ons can disrupt a lot of things, including the download process. So, you have to confirm that this is not an add-on issue. Fortunately, performing this troubleshooting process is easy in Firefox. By starting the browser in Safe Mode, you’re disabling every add-on you installed. If the error message doesn’t show up in Safe Mode, then an add-on is the problem.

These steps will show you how to start Firefox in Safe Mode:

  1. Open Firefox.
  2. Go to the browser’s address bar and type “about:support.”
  3. Hit the Enter key.
  4. Go to the top-right corner of the Troubleshooting Information page and click on Restart with Add-ons Disabled under Try Safe Mode.
  5. The browser will now restart.
  6. Now download the file again and check if the error shows up.

Refresh Firefox

If nothing works, go to the “About:support” page and click on the Refresh Firefox button under “Give Firefox a tune-up.”

Clear out temporary files

Almost every Windows application creates temporary files that become useless over time. These files can become corrupt and start causing different problems. Try clearing them out and see if the download error will disappear for good. There are various ways to remove temporary files, and we’ll be walking you through each.

Go through File Explorer:

  1. Launch a File Explorer window by right-clicking the Start button and selecting File Explorer or pressing the Windows and E keys together.
  2. Once you see the File Explorer window, navigate to the left side and click on This PC.
  3. Go to the right pane and right-click on your Windows volume, which should be Drive C.
  4. Click on Properties in the context menu.
  5. After the Properties dialog window for the drive appears, click on Disk Cleanup.
  6. After the Disk Cleanup utility scans your temporary files, select the types of files you want to delete and click on OK. Click “Clean up system files” if you’re going to get rid of system files that are no longer in use.
  7. After that, restart Firefox and check for the problem.

Going through the Settings application:

  1. Right-click the Windows logo and select Settings from the Power User menu or tap the Windows and I keyboard buttons together.
  2. Once Settings opens, click on the System icon.
  3. After you see the System interface, navigate to the Storage pane.
  4. Under your Local Disk, click on Temporary Files.
  5. After the Temporary Files window shows up, select the file categories you want to clear out, and then click on Remove Files.

Run the CHKDSK utility

Firefox might be unable to download the file because one or more sectors on your hard disk are faulty. Run the CHKDSK utility to fix that problem, then check if the file can download afterward.

Follow these steps to run the CHKDSK utility via File Explorer:

  1. Right-click the Windows logo in your taskbar and click on File Explorer once the Power User menu shows up.
  2. After the File Explorer window appears, go to the left side and click on This PC.
  3. Navigate to the right side of the window and right-click on your Windows volume.
  4. After the context menu drops down, click on Properties.
  5. Once the Properties window appears, switch to the Tools tab.
  6. Next, click on the Check button under Error Checking.
  7. Click on Scan Drive if you see the “You don’t need to scan this drive” dialog.
  8. The CHKDSK utility will now begin to scan your drive.
  9. Once the scan is complete, a dialog will appear and show you the results.

You can run a more thorough scan in the elevated Command Prompt environment. These steps will walk you through the process:

  1. Summon Run by right-clicking the Start button and clicking on Run in the Power User menu. Tapping the Windows and R keys simultaneously will also launch the dialog box.
  2. Once Run opens, type “CMD” into the text field, and then press Ctrl + Shift + Esc.
  3. Once the User Account Control dialog requests permission to run Command Prompt as an administrator, click on Yes.
  4. Immediately the Command Prompt window appears, type in the command below and hit the Enter key:

chkdsk C: /f /r /x

Note that the letter “C” in the command is a placeholder for your Windows volume drive letter.

The additional command switches do the following:

The “/f” switch prompts the tool to fix any error that it finds during the scan.

The “/r” switch prompts the tool to look for bad sectors and recover any readable information.

The “/x” switch prompts the tool to unmount the volume before it is scanned.

If the message below shows up, then the volume you are trying to scan is currently busy. Tap the Y key if the Command Prompt asks you to schedule the scan for your next reboot:

“Chkdsk cannot run because the volume is in use by another process. Would you like to schedule this volume to be checked the next time the system restarts? (Y/N)”

After pressing Y, reboot your PC to complete the check, then try carrying out your backup and check for the error.


The “Source file could not be read” issue is relatively simple to resolve. It will also help to make sure your system is adequately protected against malicious programs capable of attacking your drive. Using a competent anti-malware program that can work alongside Windows Security is a great idea.

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