Text editors

It is not so random. You can see the pattern by inserting an alert code arround line 1892:

            }
        }
alert(this.getInnerHTML());
        break;
        case "lefttoright":
        case "righttoleft":

then pasting some html text by Ctrl-V. Firefox splits up the pasted html text into chunks separated by newline codes by replacing some spaces with newlines so that every chunk has less than 72 characters. Since HTMLArea.formathtml swallows every newline code, as the result, these replaced spaces are removed.