Very high cpu usage due to Opera on desktop

I have noticed this problem for some time. It happens, for example, when I~m going through my Lifehacker feeds in Ubuntu on the Dell. For some, possibly most, feeds the CPU will go to almot 100% and then drp back to somethong like 5% for others.
I found that when it was high, I could turn off Java (Tools>Preferences>Advanced>Content) and the CPU usage would immediately go to 0-5%.
I've posted to the Opera forums to see if somebody might be able to suggest what's going on here.
More details (and a possible solution if anybody replies) are given in the thread.