To display PDF files inside the Firefox browser window, you can use the built-in PDF Viewer or a PDF reader plugin. This article covers both methods and how to fix the common issues you might encounter.

Using the built-in PDF Viewer

Firefox includes a built-in PDF viewer that allows you to view almost all PDF files found on the web without a plugin. The built-in PDF viewer is enabled by default.

PDF Viewer toolbar functions

• View document thumbnails or outline - The slider button on the far left will open a sidebar with thumbnails of the document's pages. Some documents will also have an outline view available. These make it easy to navigate through a long document.

  

• Page up and down or skip directly to a page - You can use the up and down arrows to page through a document or enter the number of the page you want to go to.

  

• Change the size of the document - Use the + and - buttons to zoom in and out or choose a zoom setting from the dropdown menu.

  

• Fullscreen or Presentation mode - Click the fullscreen button to allow the PDF file to take over your entire screen. Press ESC to exit fullscreen mode.

  

• Print - Click the Printer button to open the print setup dialog.

  

• Download - Click the Download button to save the PDF file to your computer or to open it with a PDF reader program.

  

• Copy current view - Right-clickHold down the control key while you click the current view button to open the current view in another tab or window.

  

PDF Viewer keyboard shortcuts

Troubleshoot problems with the PDF viewer

Some PDF files don't render well or are blank

With certain types of PDF files, the PDF Viewer may have problems displaying fonts, colors or the whole document. To view these files:

• Click the download button on the right side of the document header in order to open it with the default PDF program on your computer.

Cannot open any PDF files

Some extensions that block JavaScript may prevent PDF Viewer from working. You can disable them to allow PDF viewer to work:

1. Click the menu button , click Add-ons and themes and select Extensions.
2. Select each blocking extension and click Disable close to it.

For more information, see Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems.

Using a PDF reader plugin

If you'd rather not use the built-in PDF Viewer, you can use a PDF reader plugin like Adobe Reader, Nitro PDF Reader or Sumatra PDF like Adobe Reader, MozPlugger, or KParts plugin, if one is available.

To change from using the built-in PDF viewer to your PDF reader plugin:

1. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. Select the Applications panel.
3. Find Portable Document Format (PDF) in the list and click on it to select it.
4. Click on the drop-down arrow in the Action column for the above entry and select Use PDF reader name (in Firefox).

For more information, see View PDF files in Firefox or choose another viewer.

If PDF files are not displayed in Firefox, try these solutions

Check Application settings

If the PDF reader plugin comes bundled with an application, check the application preferences, to see if there is an Internet setting to to enable the plugin or to display PDF files in the browser.

Enable the PDF plugin in Firefox

Your PDF plugin may be disabled in Firefox. To enable it:

1. Click the menu button , click Add-ons and themes and select Plugins.
2. Select your PDF plugin.
3. Select Always Activate in its drop-down menu.

Reset download actions

1. Open your profile folder:

   • Click the menu button , click Help and select More Troubleshooting Information.From the Help menu, select More Troubleshooting Information. The Troubleshooting Information tab will open.
   • Under the Application Basics section next to Profile FolderDirectory, click Open FolderShow in FinderOpen Directory. A window will open that contains your profile folder.Your profile folder will open.
   Note: If you are unable to open or use Firefox, follow the instructions in Finding your profile without opening Firefox.

2. Click the Firefox menu and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu and select Quit.
3. Delete the mimetypes.rdf file.

If you still can't view a PDF in Firefox, continue with the next following instructions.

Re-initialize the plugins database

Follow the instructions in Re-initializing the plugins database.

This will force Firefox to rebuild its plugin database. If you still can't view a PDF in Firefox, continue with the next following instructions.

Re-install the application

If the PDF reader plugin comes bundled with a reader application and the above troubleshooting methods for Firefox did not work, uninstall and re-install the application.