I have been reading up on this problem as it seems there is a problem worldwide with losing Google preferences.
It happens with all browsers and all OS .

No-one, including Google, appear to have a fix for it but I came across this work around which has been working fine for me for 24 hours.

1. Enable cookies if they are turned off.

2. Go to Google

3. Click on "Preferences" on the right side of the search box.

4. Set your preferences and click "Save Preferences." You're back to the search box.

5. Click on "Advanced Search" on the right side of the search box.

6. Do not fill out anything, but just click on "Advanced Search."

7. Bookmark this new search page. (or make it your homepage)

8. Disable your cookies for Google.
Explorer 6.0 Tools — Internet Options — Privacy — Edit (near the bottom) — type in google.com — Block — OK — OK
Firefox 3.5.2 Tools — Options — Privacy — Exceptions — enter "www.google.co.th" — check Block
Opera 7.51 Tools — Cookies — highlight your google.com cookie — Delete — New — type in google.com — check Apply... — uncheck 3 Accept... — OK — Close
Netscape 7.1 Tools — Cookie Manager — Manage Stored Cookies highlight your google.com cookie — check Don't allow... box at bottom — Remove cookie — Close

9. Test your cookie block: Exit and reload your browser — go to Google — click Preferences on the right side of the search box — Google should tell you that your cookies seem to be disabled

Now when you use your new bookmark for Google searches, your preferences are passed to Google in the URL, without a cookie.
And with cookies disabled, Google won't be able to associate your search terms with the unique ID number that they use in their cookie.







If that is too complicated for you then just use this url
The preferences will probably be close to what you want
Google

and block cookies for google.co.th