Trouble with .htaccess mod_rewrite - .htaccess

Question

Please can somebody take a look at my .htaccess code to help identify what's wrong.
I am trying to amend all example.php, example.html and example.htm URL's to index.php?filename=example.html
Options +FollowSymLinks
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule ^(index\.php) - [L]
RewriteRule ^([^/\.]+).(php|html|htm)$ index.php?filename=$1.html&%{QUERY_STRING} [L]
</IfModule>
When I enter a URL like example.html I'm taken to the default 404 and not index.php

Answer 1

Try:
Options +FollowSymLinks
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?filename=$1 [L,QSA]
</IfModule>

Answer 2

I'm not using the apache .hatacces for a while,
But try this one:
RewriteEngine On
RewriteCond %{REQUEST_URI} !^/index\.php$
RewriteCond %{REQUEST_URI} !^.*/(css|img|js)($|/.*$) [NC]
RewriteRule ^(.*)$ /index.php?filename=$1&%{QUERY_STRING} [L]
Basically what you need is to be sure that the URL didn't have already index.php. You accomplish it with RewriteCond.
After you redirect all to index.php passing the filename as a parameter.
You can add more exception to the RewriteCond like on this example, all content with /css, /js, /img will not pass to this rule.
You can check this thread: Using .htaccess to reroute all requests through index.php EXCEPT a certain set of requests also