If you have increased the minimum font size then try the default setting "none" in case the current setting is causing problems.

• Tools > Options > Content : Fonts & Colors > Advanced > Minimum Font Size (none)

Make sure that you allow websites to choose their fonts.

• Tools > Options > Content : Fonts & Colors > Advanced: [X] "Allow pages to choose their own fonts, instead of my selections above"

It is better not to increase the minimum font size, but use an extension to set the default page zoom to prevent issues with text not being displayed properly.

You can use an extension to set a default font size and page zoom on web pages.

• Default FullZoom Level: https://addons.mozilla.org/firefox/addon/default-fullzoom-level/
• NoSquint: https://addons.mozilla.org/firefox/addon/nosquint/

I tried the suggestions you gave. I added the No Squint add-on. I also went to Settings/Options/Content/Fonts&Colors/Advanced, and I found that the box for "All pages to choose thier own fonts instead of selection above" was already x'd.

I went looking for pdf's as I thought maybe it happened particularly with them. Some pdf's came out fine, but there was a text-on-text problem with one, so I used the zoom out and zoom in symbols toward the top of the screen, but did not find that these at all helped with the text doubling on top of itself.

Has anyone else had this problem and been able to fix it?

Is there a bar at the top of those PDF files to indicate that there may be errors?

Current Firefox versions have enabled a built-in PDF Viewer that doesn't have all features that other PDF readers like the Adobe Reader have or may not function properly otherwise.

You can change the action for Portable Document Format (PDF) from Preview in Firefox to use the Adobe Reader or set to Always Ask in "Firefox > Options/Preferences > Applications".

You can set the pdfjs.disabled pref to true on the about:config page to disable the build-in PDF viewer.

• http://kb.mozillazine.org/about:config

You can check the value of the plugin.disable_full_page_plugin_for_types pref on the about:config page and remove the application/pdf part if present or reset the pref to the default via the right-click context menu.

See also:

• https://support.mozilla.org/kb/view-pdf-files-firefox-without-downloading-them

I finally got around to trying out your second answer, and it worked! You had said the path in Firefox was Options/Preferences/Applications. In my Firefox 19.0 there is no obvious "Options" until I click on Settings below the Google slit. Then Preferences is not there, but Applications is. From Apps I was able to select what to do. I wasn't sure exactly which one to pick, but I chose one that said to use another viewer than the one that's default in Firefox. When I did that, and when I asked for the box that notifies you each time, I tried it out at a website where I knew there were PDFs. The first I opened had a message along the top of the screen saying there might be errors, so I chose Adobe Acrobat to open the PDF instead. Suddenly the writing changed from a doubled text (text on top of text) to a nice, clear text that was easily read. I wish I had known this trick a long time ago. Thanks, Co-rel.