It's possible to save page page with Firefox CLI?
Something like:
firefox -new-tab http://google.com -save-page /path/
I'm not aware of any really simple way to do this. You might consider looking into a browser automation tool like Selenium. Alternatively, a more general automation tool like Sikuli might be workable as well (this is actually likely to be easier than using Selenium, depending on exactly what you want to do).
According to the list of Firefox command line arguments, there is no such thing.
There is a command line tool called wget (link is for Windows version, I suppose you are using Windows? If not, it's already included in every Linux distribution) which was made for exactly this purpose. Run it like this:
wget.exe -P /path http://google.com
firefox
? there are other CLI alternatives that are great for saving web pages. Even whole sites.