Red font in Firefox Page Source

Question

I have been messing around with my meta descriptions, trying to make them more unique by showing relevant data from the database.

But when I check the meta description by right-clicking in Firefox and showing the page source, the meta description tags is in red color, making me think I have made some kind of mistake.

What does the red text usually mean?

Answer 1

If you hover over that red line, Firefox gives you the answer.

It may not be easy to intepret it, but it is precise enough.