In a html-mode buffer with runs of successive <P> tags, like

    (progn
      (switch-to-buffer "foo")
      (dotimes (i 5000) (insert (format "<p> abc\n" i)))
      (goto-char (point-min))
      (html-mode))

pressing C-c C-f gets an error

    Variable binding depth exceeds max-specpdl-size

instead of going forward.  The way C-c C-f `sgml-skip-tag-forward'
requires a closing </P> etc is no doubt what's wanted for sgml, but for
the looser html it'd be good if it recognised some closing tags are
optional.