A php progrme is called from a html file but .php file does not run and want to save

I have installed lamp in Ubuntu 12.04 using these commands:

$ sudo apt-get install tasksel

and

$ sudo tasksel install lamp-server

and run the following .php file in browser and it was executed by updating database

<?php
$con=mysqli_connect("localhost","root","passwd","my_db");
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

mysqli_query($con,"INSERT INTO Persons (FirstName, LastName, Age)
VALUES ('Peter', 'Griffin',35)");

mysqli_query($con,"INSERT INTO Persons (FirstName, LastName, Age)
VALUES ('Glenn', 'Quagmire',33)");

mysqli_close($con);
?>

But when I use a .html file to connect a .php file and update mysql database the .php does not execute and want to save in a folder (Download folder as default). The .html file is:

<html>
<body>

<form action="/var/www/insert.php" method="post">
Firstname: <input type="text" name="firstname">
Lastname: <input type="text" name="lastname">
Age: <input type="text" name="age">
<input type="submit">
</form>

</body>
</html>

and the insert.php file is:

<?php
$con=mysqli_connect("localhost","root","passwd","my_db");
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

$sql="INSERT INTO Persons (FirstName, LastName, Age)
VALUES
('$_POST[firstname]','$_POST[lastname]','$_POST[age]')";

if (!mysqli_query($con,$sql))
  {
  die('Error: ' . mysqli_error($con));
  }
echo "1 record added";

mysqli_close($con);
?>

PLEASE HELP!

Solution

SOLVED! I just modified the part of the html file to,

<form action="http://localhost/insert.php" method="post">