Pressed on a dodgy link...

Better safe than sorry. Wasn't it the case on steam where links could steal your account?

It's a browser add-on that will make sure scripts/flash doesn't run on webpages unless you manually allow it. That way no malicious scripts/flash will run when you click on random links.

That's up to you. There is no 100% guarantee with an AV. Even the best retail AV programs aren't perfect. That is why the professionals recommend a multi-layered protection system. As your AV solution gets more complex, however, it becomes more burdensome. You start spending more time, money, and effort in dealing with your chosen protection.

• The simplest system is Windows Defender + MWB Anti-Malware (paid version). You do almost nothing.
• Other AV programs are available for free (e.g. Avast!), but take more fiddling with your computer.
• "Stronger" AV programs {e.g. Kaspersky) require more money, knowledge, and effort, becoming more cumbersome.

Most people use one of those three levels of security. If you need even more protection, you should be asking yourself why. Human behavior is the greatest factor in cyber-security, so that should really be your focus when it comes to keeping safe. If you are diving into seedy websites containing hacks and viruses, you are going to have issues no matter good your security is.

For the record, I use WinDef and MWB Anti-Malware.

Internet security is a serious issue in today's society.