Google Chrome Testingpage.html Opening Error

Shred here!
I want to discuss a critical problem. I am using Google Chrome as my side browser. Firefox is my default browser. Now what happened is that I received an email from Yahoo with an attachment. So, I downloaded the attachment and saved it. It was an HTML file.
The document “testing.html” could not be opened. Chrome cannot open files in the “HTML document” format.
When I double clicked the file, it automatically opened in the Chrome browser and then gave me this error message that chrome cannot open HTML format file. Firstly, I don’t understand that when Firefox is my default browser, why did the file opened in the chrome. Secondly, this error freaks me out. Why such a good browser is not able to open HTML file.
So if anyone has an answer to both of my questions, then please reply to this post.
