Could you check on whether any unexpected types of content are designated to open in the Adobe Acrobat plugin?

orange Firefox button or classic Tools menu > Options > Applications

In the Search box, type or paste adobe and pause while the list is filtered.

Most of the items should be the obvious suspects, but do any seem odd?

I do a search for adobe and get nothing.

I do get a couple of entries for Foxit, one to use Foxit reader for pdf application and the other is for saving the file.

I assumed Adobe, but yes, Foxit is the right search here. It's normal to have Foxit (or Adobe) for PDF files. What is the other entry? Usually there is a "mime type" listed in parentheses, such as "(application/x-pdf)"; if the description is too long, it should appear in a tooltip if you hover your mouse over the entry for a while.

Content type Foxit pdf type (binary octet stream) Action-save file

Content type Foxit pdf (application/pdf) Action-Use Foxit reader 5.3

Hmmm, it doesn't seem like there's anything wrong there. You could clear all customized settings on this tab and let Firefox rebuild them. Save all work (e.g., email messages or posts you're composing, documents you're editing), then in this article, see the section captioned "Reset download actions for all file types":

What to do if you can't download or save files

Note: starting in Firefox 12, the button changed from "Open Containing Folder" to "Show Folder".

Does that help?

Just saw this related thread: Foxit Reader spews a lot "not a PDF" on some pages. Matt_G suggests rolling back to an earlier version (and gives a link for instructions).

You can also look at this extension (part of Firefox 15+):

• PDF Viewer: https://addons.mozilla.org/firefox/addon/pdfjs/

I don't have any proof yet, but it seemed to start happening for me when I updated to the latest Adobe Flash (at least I think it was Flash). I know the updater tells me a new version is available and at this point I just install it. I don't think I was having the problem right after installing FF13, so I give it a 90% chance that it's due to Adobe. I've restored my computer back to FF12 and when I get the time I'll try updating to FF13 again and see if it happens again. Hope this helps somebody.

Well it hasn't done the error for the last few days and I have not made any changes to the system except to install v. 2.2.2 of the Search Menu add-on because v.2.2.1 wasn't working with FF13.

Weird.........

Had the same problem. I upgraded to the newest Fixit Reader (v 5.3.1.0606), and presto, problem resolved! Thank you Mozilla!