No the unresponsive script warning is not coming up.
But the pages hang for anything up to a full minute till the advertisement loads.
SO the page opens with all of the forum text and forum graphics quickly
Usually the side bar adds load first
then everything comes to a halt while the adds that appear horizontal load.
I tried using a fresh copy of Firefox with no browsing history and the cashe cleared and that loaded quite fine.
SO the problem appears to be Google snooping around on the hard drive to work out which advertisements to load.
Most of the side bar ( vertical ) adds seem to be general , forex trading , generic drugs, womens fashion and other junk sold world wide
All of the horizontal adds are location specific and in my case my computer specific because it is showing adds for stings I have looked at on ebay , gumtree and stuff I have ordered from my suppliers directly from their web portal.
On the computer with nothing on it the adds in the vertical & horizontal containers were roughly the same.
For example this morning I hit the unread tag then opened the 35 posts in separate tabs.
This took about 2 minutes to do because the unread posts tab continually hung.
I then went to the toilet , then into the kitchen, made a coffee ( 3 minutes ) put the oats on to cook , came back in and the tabs were still loading.
Struggled through the first 5, then took the oats out of the microwave ( 5 minutes cooking time ) came back and according to firefox all the tabs had finished loading.
When going through them it was still sluggish till I got to the 13th tab by which time the forum behaved as it used to.