I was trying out ExploitShield by ZeroVulnerabilityLabs https://www.wilderssecurity.com/showthread.php?p=2122261#post2122261 & visited lots of infected www's. Quite a few were intercepted my WSA some by my ISP & all the others failed to work ! That's after allowing Scripts/iframes etc. Of course i have no Java on here but not all were Java exploits. Anyway, on the ones that WSA noticed, i saw a Too quick to see/read flashing box appearing every few seconds in my top left screen. Only after i minimised a few FF windows was it able to become stationary, & then i could select my options. Even after allowing through WSA, nothing worked ? Not that i'm complaining Is this a bug, or ?
This is probably a rendering/UI issue - it would be worth seeing what it behaves like in a more simplistic environment (just a couple open tabs and not trying to bombard it with exploits ). There were some issues previously with the block dialog but they should be fixed in most cases now.