If you get a page from your ISP then your ISP might be intercepting the DNS request and automatically redirect you in case a DNS look up fails.

You can contact your ISP and ask for a DNS server to opt-out of that feature.
You can check if there is a link on the search results page to go to your ISP and opt-out.
You can set different DNS servers.

• http://kb.mozillazine.org/Error_loading_websites#DNS

That helped. I now don't get my ISP! However, I now get

The connection was reset

The connection to the server was reset while the page was loading.

   The site could be temporarily unavailable or too busy. Try again in a few moments.
   If you are unable to load any pages, check your computer's network connection.
   If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web.

Instead of going to Google search. Any ideas?

Try with all plugins disabled and in Firefox's safemode. Maybe some of your addons are part of the problem. Also check what search engine is selected in the searchbar as Firefox now uses that search engine for all searches.

• Diagnose Firefox issues using Troubleshoot Mode
• Search bar - add, change and manage search engines on Firefox

I've used safe mode & reset - neither worked.

What changes did you make?

Are you using a direct connection?

• Tools > Options > Advanced > Network : Connection > Settings

use system proxy settings