From mozilla. I'm guessing that the links were hosted/owned/etc. by google. When your system resumed it only partially loaded the sponsored links and you were left with the text of the url.
Your system is fine security wise, but privacy wise pinging google servers everytime you open a new tab is not ideal. This type of stuff is why I use Librewolf. Of course it's up to you how much it bothers you. You can disable alot in vanilla firefox too.
Install clamav and run a scan. You will probably get false positives.
For instance the gnome polkit agent has a "malicious" image that it tries to load at start and if it succeeds it kills the program before it can run. This is to keep an actually malicious icon from being used. I spent days on that one lol
Depends on the malware database you use, but out of the box it'll catch wide range of stuff, even linux malwares (which is rare but exists and mostly infect vulnerable web servers).
You're saying even if you're not confirmed as infected, you're not necessarily confirmed as not being infected. In other words, you're talking about false positives.
I think you're on the same page, but mean false negatives not false positive.
False negatives being the potential that you have the virus, but the scanner wasn't able to identify it so returned a "you're all clean" when in fact, you've got a dirty virus and should have listened in health class.