Guest and BillD, it is not a question of browsers, it is a question of the HTML standard.

In HTML 4.01 it says in Chapter 3.2.2:

By default, SGML requires that all attribute values be delimited using either double quotation marks (ASCII decimal 34) or single quotation marks (ASCII decimal 39). Single quote marks can be included within the attribute value when the value is delimited by double quote marks, and vice versa. Authors may also use numeric character references to represent double quotes (") and single quotes ('). For double quotes authors can also use the character entity reference ".

In certain cases, authors may specify the value of an attribute without any quotation marks. The attribute value may only contain letters (a-z and A-Z), digits (0-9), hyphens (ASCII decimal 45), periods (ASCII decimal 46), underscores (ASCII decimal 95), and colons (ASCII decimal 58). We recommend using quotation marks even when it is possible to eliminate them.

Your url contains a slash, a slash is not listed above, therefore, the value of the href attribute has to be quoted.

When using the even more modern XHTML, every attribute value has to be quoted (see Chapter 4.4 of XHTML 1.0):

All attribute values must be quoted, even those which appear to be numeric

And yes, the Mudcat FAQ says the quotes are optionally here in the Mudcat, but this is one piece of the FAQ that I do not agree with - correct HTML should always be used as incorrect HTML can lead to more browser problems than correct HTML.

MudGuard