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