Validate HTML

you need to validate the generated html, not the jsp source files.

>> Copy the HTML out and paste it in a HTML file?

That will be real pain. Since the JSP's are huge with lots of HTML in it. Is there a way which ignores JSP and just validates HTML.

> Is there a way which ignores JSP and just validates HTML.
No, there is no way!!!  You need to validate the generated HTML, not the source code.  How do you expect a validator to know what HTML will be generated by your jsp source file?

You can also use another Firefox extension called Web Developer (https://addons.mozilla.org/firefox/60/) that has an option to show generated source code. Just copy&paste that generated source code into W3C Validator.
I have used this successfully many times while developing a JavaScript web applications.

CyberGhost, jsp is server-side!!!
And note that you can see the generated code (after javascript / xsl) in firefox just by doing select all (ctrl+a), then right click and choose "view selection source".  That's exactly what the webdev toolbar does.

GrandSchtroumpf: you're right, I was probably trying to answer too many EE questions at once and thougt I'm back in the JS section :-)
Sorry about that.

thomas908: please, ignore my comments

JS / JSP, the difference is just one letter :°)

Eternal_Student has a good point, thats what I would try

> Eternal_Student has a good point, thats what I would try
that's a lot of copy/paste.  using the ff extension is easier.  also the webdev toolbar has shortcuts to validate html usin the w3c site.

Thanks a lot everyone. Please give me day to close the question.

Thanks everyone for helping.