When I was a kid I visited my grandparents and since there was still only Internet Explorer on their terrible computer I decided to install Firefox.
Unfortunately the computer power supply died right after I did.
Therefore my Firefox installation was determined to be the root cause of the computer being ruined.
So yeah, Firefox apparently kills power supplies in some folklore.
What you can probably do is create an encrypted archive and selecting the checkbox that hides filenames. It's what I usually do in that type of case.
It should prevent gmail from knowing what is in the archive.