Sounds like a Widows user. I didn't do anything! well I did that and that and that. But I didn't think it would cause a problem!
Pretty much all free software wants to send data to its host website and affect your computer somehow.
You allow Firefox to access the internet so any add ons have access to the internet too.
Its a good thing Linux is Virus proof except when you install software and Firefox is safe except when you install add ons.
We are the LinuxMint. You will be assimilated. Resistance is futile.