Process HTML files like PHP

You need to add

AddHandler application/x-httpd-php .html .htm

Try this:

AddHandler application/x-httpd-php .html .htm

or

AddHandler x-httpd-php .html .htm

or

<FilesMatch "\.(htm|html|php)$">
SetHandler application/x-httpd-php
</FilesMatch>

or

<FilesMatch "\.(htm|html|php)$">
SetHandler application/x-httpd-php5
</FilesMatch>

Edit: For 1&1 server:

AddType x-mapp-php5 .html .htm

One of these should work