example:

Try to use the search function in
http://www.stevehoffman.tv/forums/index.php

Workaround: Copy the link with 'c' and open a new buffer with 'C-u y'

I can use the search function at that forum by the following steps:

 1. hit 'f' and select the "Search" link
    a DOM popup appears with the search field.

 2. hit 'tab' to focus the search field.

When I reproduce your steps, the popup disappears after hitting 'tab' and the modeline reads "form/text"
in white letters over blue as background colour, but only for a couple of seconds.

If I type some string to search for (assuming the popup is there yet "invisible"), nothing happens. Then
I have to type 'esc' to unfocus and continue browsing.

Alright, after some more testing, it has to do with my .conkerorrc dir, hence it is most likely not a bug

Keep us informed of what you find in your config that could cause the
behavior you see.

Let's be clear, the steps I posted are a workaround for the specific case,
not a general solution.  A perfect solution will be very hard to come by
because the website is using javascript (the YUI library, it appears) to
create GUI-like features through event-listeners.  What events it is
responding to is hard to say without a deep inspection of their
javascript, but if we knew, there might be steps we could take to
intercept and block those events when hinting was active, in some cases.
The entire topic is one of exceeding complexity.