Q:

Command to run html with php script

Can anyone tell here, what is the command to run html with php script. Normally in my linux terminal, if i want to run html, my command is
firefox <filename>.html

It works fine and display output in firefox browser. But some how, when I add php script, the browser doesn't show the output from php script. It show source code. I try the answer from the forum below, it doesn't work for me.
Using .htaccess to make all .html pages to run as .php files?
How to run a php script inside a html file?
So here, i want to ask
1) What is the step to run html with php script
2) what is the command to run?
3) The source code, need to save in .html or .php ?
Is there any way to run php in browser without using apache?

A:

Rename file.html to file.php and check. 
I think you write PHP and HTML in a single document, and you use only html extension.

