Thank you for attempting to help.
I tried entering "Set up guest user" in Help but got "The selected topic is currently unavailable." Interesting.
This has happened on a number of occassions - this message.
Anyway I had guest user already active so I logged in as guest user.
As guest - the web pages opened fine.
I tried booting in safe mode according to the Apple instructions. You had said that this would be much slower. Well, after 20 minutes I shut it down.
I had read another way to safe mode boot was by holding the Shift key down until the words "Safe Boot" in red lettering appeared. Holding the shift key down I didn't see the words appear - but I did get a "thermometer graphic" showing loading and then the log in screen appeared. I presume this was safe mode.
In safe boot mode the web pages were defective as before.
Any other ideas?
Wow. I was beginning to think - "this is like working with Windows!"
Anyway, I got a good night's sleep then took a deep breath.
Here were results from following latest post.
Safari didn't appear in Force Quit menu after quitting Safari.
Open in 32bit mode was not checked.
I clicked Delete All in Flash Player Advanced preferences. (Deleted the first group - not the second.)
Went to Library and moved files to a desktop "removed" folder. (WebKit.PluginProcess, WebKit.PluginHost, and Safari.savedState files didn't exist.)
Tried Safari - still the same problem!
Entered rm command in terminal. (note: in my terminal lines don't end in $, they start with HomeFolderName:%.
Launched Safari - still the same problem!
Moved these files to my "removed folder" on desktop.
Tried again. SUCCESS! Apple website pages now showing up properly.
Finally, I was able to restore Bookmarks by removing the new Bookmarks.plist from the Safari folder and putting my old file from the desktop in it's place. This seems to have worked fine.
My old settings for user names and passwords were not affected.
As for extensions - I'll be very careful in the future.
I previously had had a problem with pdf files from Safari not being able to be saved without corrupting them.
In that case I had removed adobepdfviewernpapi.plugin and adobepdfviewer.plugin from the internet plug-ins.
Thanks for all your help!