Safari force reloads tabs, works slow, half opens webpages, unclickable links

Question

I am running Safari Version 6.0.5 (8536.30.1) on OSX 10.8.5. Then out of a blue pages in Safari started loading eternally slow. Either the blue line over the webpage address would start running and freeze with a simple site site loading minutes, or a site would load actually more or less ok but after scrolling down:
- many links would become unclickable as if there were any
- the webpage would load, but after scrolling back and forth part of it would turn white and not scroll down any more, although it did show the whole page just moment ago
- part of the page loads and other part is displaid as white space.
Resetting Safari, clearing Web site data and cookies, CleanMyMac-ing, all these to no avail. At some point playing around and trying to load different web sites in Safari I got the following message:
Webpages are not responding. To visit the selected webpage, all webpages in other tabs and windows must be force reloaded. Do you want to visit this page? Force reloading might lose information you've entered.
with CANCEL or VISIT PAGE to react. Clicking on either did not resolve the problem.
I have neither installed any software nor Safari extensions. Except maybe the most recent OSX update yesterday which was necessary for iTunes getting iRadio. Google, Opera, Firefox are all running perfectly just like Safari has been doing until today.
Any idea what is wrong?

Answer 1

Please read this whole message before doing anything.
This procedure is a test, not a solution. Don’t be disappointed when you find that nothing has changed after you complete it.
Step 1
The purpose of this step is to determine whether the problem is localized to your user account.
Enable guest logins* and log in as Guest. Don't use the Safari-only “Guest User” login created by “Find My Mac.”
While logged in as Guest, you won’t have access to any of your personal files or settings. Applications will behave as if you were running them for the first time. Don’t be alarmed by this; it’s normal. If you need any passwords or other personal data in order to complete the test, memorize, print, or write them down before you begin.
Test while logged in as Guest. Same problem?
After testing, log out of the guest account and, in your own account, disable it if you wish. Any files you created in the guest account will be deleted automatically when you log out of it.
*Note: If you’ve activated “Find My Mac” or FileVault, then you can’t enable the Guest account. The “Guest User” login created by “Find My Mac” is not the same. Create a new account in which to test, and delete it, including its home folder, after testing.
Step 2
The purpose of this step is to determine whether the problem is caused by third-party system modifications that load automatically at startup or login, by a peripheral device, or by corruption of certain system caches.
Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards. Boot in safe mode and log in to the account with the problem. Note: If FileVault is enabled on some models, or if a firmware password is set, or if the boot volume is a software RAID, you can’t do this. Ask for further instructions.
Safe mode is much slower to boot and run than normal, and some things won’t work at all, including sound output and Wi-Fi on certain iMacs.  The next normal boot may also be somewhat slow.
The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.
Test while in safe mode. Same problem?
After testing, reboot as usual (i.e., not in safe mode) and verify that you still have the problem. Post the results of steps 1 and 2.