Trouble viewing PDFs in Firefox (Windows)


PDFs don't display or you receive an error that Adobe Acrobat/Reader cannot display PDFs in the browser. (Chrome users, see our help article Trouble Viewing PDFs in Chrome(Windows).) If you are having trouble viewing PDF's with Safari, see our help article entitled Safari on the Mac logs me out of Merus every time I open a PDF.


Is the problem is localized and only on your computer? If it is, then you know there is not a problem with the file, or with MerusCase delivering the file, but with your computer or the browser settings. 


If the problem is reproducible on multiple computers, then there may be a problem with the file. Please contact MerusCase Support for assistance by filling out the contact form at the bottom of this page.


Restarting Firefox may fix the problem.


Check Firefox settings

  1. At the top of the Firefox window, click on the Firefox button (Tools menu in Windows XP) and then clickOptions
  2. Select the Applications panel.
  3. Find Adobe Acrobat Document in the list and click on it to select it.
  4. Click on the drop-down arrow in the Action column for the Adobe Acrobat Document entry and select Use Adobe Acrobat (in Firefox).

    • If Use Adobe Acrobat (in Firefox) is not listed as an Option, see Reset download actions below and then repeat this set of instructions.

 5. Click OK to close the Options window

Now try to view a PDF in Firefox. If it opens in the browser window, the problem is solved. If not, continue with the following instructions.

Check Adobe Reader settings

  1. Open Adobe Reader.
  2. Once in Adobe Reader, click the Edit menu in the menu bar, and then click Preferences... The Preferences window will open.
  3. In the Categories section, click on Internet.
  4. Make sure the first check box, Display PDF in browser, is checked.
  5. Click OK to dismiss the Preferences window, and then close Adobe Reader.
Now try to view a PDF. If it opens in the browser window, the problem is solved. If not, continue with the next troubleshooting instructions.

Re-install the plugin

  1. Close Firefox.
  2. Open the Adobe Reader installation folder. This can be done by using Windows Explorer to navigate to C:\Program Files\Adobe\Reader 9.0\Reader\, assuming Reader 9 is installed in the default location.
  3. Open the Browser sub-folder inside the Adobe Reader installation folder.
  4. Copy the nppdf32.dll file to the Firefox plugins folder: Right-click the file and then click Copy from the context menu. Then use Windows Explorer to navigate to your Firefox installation's plugins folder (e.g.C:\Program Files\Mozilla Firefox\plugins). Right-click in the file list and click Paste.
  5. Open Firefox and in the address bar type about:plugins to bring up the Firefox plugins list.
  6. Look for the Adobe Acrobat entry.
If the entry is there, try to view a PDF. If it opens in the browser window, the problem is solved. If not, follow the next set of troubleshooting instructions.