<IfModule mod_rewrite.c>
  RewriteEngine on

  RewriteCond %{REQUEST_URI} !.*.
  RewriteRule ^(.*) /$1.htm [L,QSA]
</IfModule>

RewriteEngine on

RewriteBase /

RewriteRule (.*)/$ $1 [L,QSA]

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !.htm$
RewriteRule ^(.*)$ $1.html [L,QSA]