Why do these symbols appear ’instead of '?

Hi there we have the message read. This can be caused by certain topics. Receiving infected emails with which text is sent that may have been copied from an infected notebook that was or is being used by others. You can also use a lot of translated text in other languages ​​such as Chinese or something else? The values ​​of the text editor must be set to utf-8. Can you do this text easily erase after each receipt of this? And continue without it? Greatings Firefox volunteer.