Connection not secure on well-known sites
I have noticed that recently a lot of well-known and trusted sites(eg- youtube) are showing connection not secure (Parts of page are not secure such as images and any information that you share may be leaked -passwords etc) . Sometimes when I reload the site, it again shows connection secure.
Is this a glitch or something to be worried about and is there a solution?
Firefox Version - 88.0.1 (64-bit) OS- Ubuntu 20.04.2 LTS
There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.