A fellow named Kevin Basil seems to agree with mpt that the lack of a notification to the user that the a page has invalid markup is "a top usability problem for Mozilla ... because it prevents users from using the browser for their daily operations." The problem is that most users don't care why the page isn't working. They care that the page isn't working. Telling a user that he can't use Mozilla to do his banking because his bank wrote the page to work with IE (which is a far cry from mpt's call for a notification "to list the errors in a Web page") simply doesn't make Mozilla more usable. Until he can actually use his bank's web site to do his banking the browser is unusable and no amount of explaining where the blame lies is going to change that. Like Tim Powell says of this indicator, "users will think it reflects their feelings and will do nothing to help them."
Mr. Basil then says "mpt is simply suggesting a simple element in the UI to indicate to the user when the problems are not Mozilla's fault." But as I hinted above Mr. Basil is actually making a different argument than mpt. Mpt is calling for a notification "when a viewed web page contains errors". He is not calling for a notification when a web page is not behaving as expected in Mozilla because the author wrote the page for IE. There's a very big difference between those two.
Anyone that wants to run 50 of his bookmarked sites through the W3C HTML validator will see how quickly an indicator like mpt has suggested becomes almost completely worthless. A majority of the pages I visit regularly have errors. Mpt's error indicator would therefor be active on the majority of pages I visit, even pages which appear to work just fine. There are also pages which validate just fine but contain sufficient real HTML errors (like using alt text for something other than it was intended and failing to use the title attribute correctly) that they are considerably less usable in Mozilla than IE. Mpt's indicator would do nothing for those pages.
This feature request, to visually indicate to the user when a page uses invalid markup, is a fine idea and I support it. I think something like that would be nice. I dispute, however, that it will make the browser significantly more usable for average users or that it belongs in a top 10 list of usability problems with Mozilla. I don't dispute that pages not working for users of Mozilla and Mozilla-based products is a major usability issue. I agree completely. As a matter of fact, if mpt had said that the number 9 usability problem is that pages don't work well in Mozilla I would have said "that's number 9? why not number 1?" But mpt wasn't saying that. He was saying that the lack of a validation indicator was the number 9 usability problem in Mozilla. I don't believe that an indicator makes broken pages any more usable. I also assert, again, that adding a validation indicator would do far less for Mozilla usability than improving the current plug-in experience.
