here is my configuration:
I would like thank Everybody for this post as it really helped me a lot and I used something like the one below and works for me ...
Options +FollowSymLinks -MultiViews
RewriteEngine on
RewriteBase /
RewriteCond %{ENV:REDIRECT_END} =1
RewriteRule ^ - [L,NS]
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule ^(.*?)\.(php|html?)$ $1 [R=301,NC,NS]
RewriteCond %{REQUEST_FILENAME}\.html -f
RewriteRule (.*)$ $1.html [L,E=END:1,NS]
RewriteCond %{REQUEST_FILENAME}\.htm -f
RewriteRule (.*)$ $1.htm [L,E=END:1,NS]
RewriteCond %{REQUEST_FILENAME}\.php -f
RewriteRule (.*)$ $1.php [L,E=END:1,NS]
This version works for me.
Thank you.
Cheers!