Marquee -- I haven't seen that in years.
That element is not valid HTML 4.x or later having been deprecated some time ago. This means that browsers may drop support for it in the future, your pages will not validate now, which forces the browser into quirks mode and may cause unpredictable layout bugs to crop up from browser to browser.
For the record, the tag was never part of a valid HTML spec, but an IE proprietary tag. That it works at all in any other browser surprises me a bit.
My advice would be to drop usage of the tag along with blink, under construction gifs and other gimmicks from the 90's. Moving text is EXTREMELY distracting on a website and brings up major usability concerns, not to mention making the printing of the page difficult to impossible, depending on the amount of text in the marquee.