I finally solved the problem with the Selenium testing. The problem wasn’t because of the “Failed opening ‘SiteTest: Firefox.php’” at all. It was just a warning message. The real problem is the curl extension in PHP. I thought I already enabled it, but not when the CLI version is not using the same ini file. So, after I enable the curl in the CLI version of the ini file, it works fine.
I’m still wondering though, how do I make the CLI version use the same ini as the web version.