*caveat - I haven’t tested the below, as I don’t have time to break my dev site*
If you’ve removed the HTML content type, then I’m not sure simply replacing a new Content Type key of HTML is going to help - as the content type key (1, in this case) is hard-wired into the site_content table. If you add another Content Type in System > Content Types it will presumably auto-increment the key.
You’ve got two MySQL options - (i) Create a new content type key, check what ID it has, and then update all site_content resources with id of 1 to this new number, or (ii) Create a new key, and brute force the ID back to 1 (it may not allow you to do this).
As for your initial question, I take it you wanted:
http://www.foo.bar/friendly.html
to become:
http://www.foo.bar/friendly
Depending on how big your site is, you can do this by checking the container box on a resource, and changing the container suffix to blank in Friendly URLs. Or as the original respondent suggested, by making the HTML content type have a ’blank’ suffix.
