You need to download the message bodies, not just the headers. This is done by enabling synchronization, i.e. 'Select this newsgroup for offline use'.

I did as Christ1 suggests. It synchronized. The filter options are still the same (Subject,From,Date,Size and Customize). How do I get a filter to operate on the now downloaded contents of the articles.

Regards JC......

You need to use a Custom filter. Try this:

Tools (Alt-T) > Message Filters > New

Now where it says Subject, click on it and select Custom

When a new window opens, type Body (to say body contains something ...).

At the end it should looks like this: http://s3.postimg.org/cnp78odxf/Screenshot_from_2015_10_01_01_23_00.png

Why do you want to filter the message body in the first place?

Hi Chris1. I did as much as you suggested. Still the filtering did not work. There is possibly an attachment (very similar to yours and another filter I have for the Subject). The other filter I have for Subject works OK.

The pathway to do this seems cryptic (having to enter a key word like "Body" in a manual manner).

My reason to do this is to identify very old articles I have on Usenet where I sign off "Regards JC...".

Regards JC.....

Hi Mozilla. I still have issue with filtering on the content of Usenet articles. I don't believe it works and the idea of a customized keyword "Body" with the interface deserves further explanation.???

Regards JC......

Your topic title said "search" but I find we're talking about filtering.

Since this sounds as if it might be a one-off recovery operation, a true search using the Global Search, or the QuickFilter might do a better job of searching and locating your downloaded news articles. Having found all your postings, you could then try to do something with them en bloc, but TBH I'm not sure what you can do with newsgroup articles. It is very much a server based system, and dates back to times when local storage was expensive and therefore scarce.