Safari 6 Unresponsive Scrolling and Bookmarks Bar Problem

I installed Safari 6 on my MacBook Pro 17 with OS 10.7.4 8GB RAM, 1TBHD (600+GB free) and all seemed well for a week or so but a couple of days ago I noticed that the scrolling seemed very sticky in that I'd be scrolling down a longish page and suddenly my two-finger scrolling movement would not work for one swipe but would work the next. At first, I thought that maybe it was my fingers being very dry or the trackpad was dirty but it only happens in Safari.

But about the same time something else started to happen. When I click on a folder of bookmarks in the Bookmarks Bar, instead of getting the dropdown list of bookmarks in the folder, all the bookmarks would open in tabs. The first time this happened, again, I thought I had mistakenly clicked the folder with two fingers and selected 'Open in Tabs' - but it has happened quite a few times over the past two days and I have been careful to observe that I am not using two fingers nor is the menu which has 'Open in Tabs' even appearing - I am literally just clicking the folder title.

Perhaps it is only co-incidental but I have also noticed that typing text in a field in Safari is also a little slower (as it is typing this with an occasional latency of about half a second.

I read in another thread that a similar scrolling problem was resolved by repairing disk permissions but this did not work.

I have also emptied Safari's cache and deleted its preferences but without success.

Any ideas anybody, please?