The site which 'objected' is
Motorsports At VIPLeague And Vipbox - and I've discovered I was using Opera rather that Firefox - sorry.
I've just re-activated Adblock Plus (in Opera) and the intrusive message returns (for that site). It never used to 'object' - this is a very recent development.
No locking - just a persistent advert that doesn't go away and can't be removed by clicking a 'cross' as was usual previously.
What do you mean by 'accepting the download'.
I cannot 'close' the advert - the only option permitted would be to click 'yes' and follow the download.
It annoys me that AdBlock Plus no longer works for
http://www.vipleague.is/sports/motorsports.html]