The code that Flash outputs is not standards compliant and embed tags do not validate because they are not part of the XHTML standard.

Note: The following series has been consolidated into one article here. Dump the WYSIWYG Do not use markup for presentation Include a proper doctype Validate your markup Validate your CSS Build for Firefox and hack for IE If you have a problem ask for help Let’s go through each of these steps in greater detail

Let’s face it. You can either be a part of the problem or a part of the solution. If you are allowing an application to turn out your markup then, unfortunately, you are a part of the problem. Yes, this includes Dreamweaver and GoLive. I am thoroughly convinced that these “web page editors” are for [...]

Tables are meant to be used for one thing and one thing only and that is the display of tabular data. Please, do not use tables for layout. It is much better left to CSS. Using tables for layout is a messy hack often used to “get pages to look the same in all browsers”. [...]

You start your sentences with a capital letter; start your HTML with a DOCTYPE. It’s just basic grammar. – Mark Pilgrim from Dive Into Accessibility Using a complete doctype will switch your browser into standards mode. This will cause it to render the page exactly as you have instructed it (which may look awful but [...]

Developing a website without validating is like running around with a blindfold on. As soon as you ask for directions, don’t be surprised if the only answer you’ll get is “take your blindfold off”. – some guy named Jim Validate your markup here Validate your CSS here

Firefox is a standards aware browser. The authors are actively involved in squashing bugs and making it work the way it should. When FF is switched to standards mode with a proper doctype everything works as expected.

IE is the bane of every serious web designer. Some things you are going to want to look up are peekaboo bug line-height bug guillotine bug duplicate character bug italics bug double float margin bug three pixel jog escaping floats bug creeping text bug These are addressed at Position is Everything

The steps before this one are necessary. Good clean code is hard enough to debug. Code with bunk markup and presentational hacks just throws more hay on top of your needle. Taking the steps above before asking for help shows that you are at least trying. To drive that point home here is one of [...]