@sophia let me tell you something. if you think i'm going to let you get away with spreading lies then you're wrong.
gmail isn't FOSS.
FOSS is stuff like microsoft edge and apple safari because they're free and let you open the source code of the website by clicking view source, makin them Free "Open (the) Source" Software - FOSS
There's a very strict definition of Free Software, as well as OpenSource, and so F[L]OSS as well.
And they include publishing the source code of the software.
What you see in the browser is the code of the pages that are generated by it, not its own code.