I'm having similar problems with Firefox 4 under Ubuntu 11.04.
Nearly every second button/link/text box can't be clicked/used and sometimes buttons/links/boxes can only be clicked/used in some parts of the button, box or underlined text. Sometimes it help to scroll down and up again on the same site, sometimes I have to reload the page (and, finally, very often I have to use Opera, which works perfectly under 11.04).
I'm having similar problems with Firefox 4 under Ubuntu 11.04.
Nearly every second button/link/text box can't be clicked/used and sometimes buttons/links/boxes can only be clicked/used in some parts of the button, box or underlined text. Sometimes it help to scroll down and up again on the same site, sometimes I have to reload the page (and, finally, very often I have to use Opera, which works perfectly under 11.04).