An example just showed up on here:
I see the text as starting with a ( followed by a square that has 23 on top and 18 on the bottom and the same thing shows up in the first paragraph of the body.
I have seen this sort of thing at various places around the web, it seems to happen mostly in things I believe were prepared in a word processor.
When it happens it can at times happen so much that the page is hard to read. Many of the offending boxes (they don't always contain the same numbers) seem to occur where apostrophes should be.
Google seems to say this is what Firefox does when it can't render a Unicode character but why is this happening and what can be done about it?
Edit: The answer I accepted fixed only some cases, not all of them.
Some examples that remain:
By context I think these are an apostrophe, an opening quote and a closing quote.