Thanks to Matt for an understandable explanation of some weird characters within our incoming email. We rest assured the quirks in our incoming email text is not attributable to our PC's settings. Sadly, I doubt Apple cares sufficiently to make an effort to correct concerns they created for Windows users. Perhaps we will be unhappy enough to buy an Apple devise. Hmm, no chance!

I have had the same problem with the  character inserted into emails that I have received from some others, and almost always those I have received from myself. I am on WinXP SP3 with whatever are the final updates available there, I am running Tbird 31.1.1 . Mozilla seems to have made changes to how it handles ( or now, mishandles) font displays. I have made no changes to my system's display settings until trying to correct this rather recent problem. Again, I have never seem these odd characters ( and others) until recently, and they come from within my own system.

My Tools>Options>Display>Formatting>Advanced>CharacterEncodings settings were originally: Outgoing Mail: Unicode (UTF-8) Incoming Mail: Western (ISO 8859-1)

Per the suggestion above, changed both to Unicode (UTF-8). That did not solve the problem.

Then I changed so both are Western (ISO 8859-1). That seems to have solved the symptoms.

However, I do not think it has solved the problem. Mozilla has evidently made a change to their systems which affects the display of fonts, even those sent from my system to itself when I have made no changes to my configuration during that time! Pointing to other software vendors' non-standardization is, at best, an incomplete explanation for this issue. This is a recent issue that has cropped up during Mozilla's apparent frantic efforts to get those version numbers to triple digits before 2016 for no clear and valuable reason.