Beginning with version 19, Firefox added its own PDF viewer, which doesn't always render some fonts correctly.  More than likely, your Firefox browser is using the built-in PDF viewer instead of the Adobe Reader (aka Adobe Acrobat) plugin to display PDF files.  To switch from the built-in viewer to the Adobe Acrobat plugin:

1. Make sure the latest version of the free Adobe Reader is installed on your computer. Here are a few ways to check:

• Find a PDF file (file name ending in ".pdf") on your computer and double-click it.  If the file opens and you can view its contents, you have Adobe Reader.
• Look on your Start Menu for Adobe Reader.  If you see Adobe Reader, you have Adobe Reader.
  
• Click Start, and in the search programs and files field, type "Adobe".  If you immediately see "Adobe Reader XI" (or a different roman numeral), you have Adobe Reader.

2. If you don't have Adobe Reader, click this icon  to download it and install it.

3. After verifying that Adobe Reader is installed on your computer:

1. From the Firefox main menu, select Tools > Add-ons and click Plugins on the left.
2. You should see Adobe Acrobat in the list of plugins and to its right the pull-down tab should say "Always Activate".  If not change it to "Always Activate".
3. Close the Add-ons Manager.
   

4.  From the Firefox main menu, select Tools > Options and click the Applications Icon (in the row of icons across the top).

1. You should see something like this:
   
   
2. In the Search field, type "pdf" and you will see:
   
   
3. Under Action, select "Use Adobe Acrobat (in Firefox)":
   
4. Click OK.

That's it!

Now go back to view your PDFs in Firefox.  If open, close them and then re-open.  Your fonts will look and print correctly.