Thanks. Over 10 years ago, Firefox was the recommended browser for the Mac. So, the situation has changed?Had this problem with Firefox often. I don't think it's been particularly well optimised for the Mac. I have since switched to Safari which works far better with less overheating. Give it a try.
I know how to export but I am concerned about messing up everything when the bookmark folders in FireFox and Safari have the same name. I am also concerned that they overwrite each other.