Weird Characters in Firefox and Chrome

[Robi]

Both the browsers windows and all their various "Options" and "Book Marks" show little squares with a horizontal line through the middle with a letter above it and a two digit number below. These browsers are both the most recent releases. When I manage to get a web page to load in either one of these browsers (my entry into the search box appear in the weird characters) the text on them is in English and everything works fine, such as Amazon Prime Movies or Britbox.

[Robi]

I didn't have my glasses on! The boxes don't have a horizontal line. They all have "00" in the top half (I'm guessing that's zero, zero) and some have a number followed by a letter and all others have only two numbers below the "00". Those two characters might be hexadecimal or some other code, none of which I understand.