I am using the latest version of Eclipse Luna (for Java EE developers), and when I insert an
<input type='text' placeholder='test123'
Eclipse checks for html tags and attributes against the doctype. Make sure that you have given doctype on top. It will fix the problem. Also, Eclipse uses IE internally. You can configure it to firefox/chrome for better tags and attribute comparison.
Refer to this How can I change eclipse's Internal Browser from IE to Firefox on Windows XP? for changing your browser.