I had been using Chrome on my Samsung S10 but then the text became too tiny.
I switched to Firefox and it is normal size. I figure Firefox notices the missing meta name just like when a webpage title has a space and the web browser inserts a non breaking symbol in so it loads.
I switched to Firefox and it is normal size. I figure Firefox notices the missing meta name
You are right.
The problem is that FR is missing a critical tag in the <head>:
<meta name="viewport" content="width=device-width, initial-scale=1" />
Every website since 2015 should always include this tag.
It is a very simple fix.