Just Windows Security?  

Check Malwarebytes Browser Guard. It is an extension that checks things at the Browser level.

Has a version in the Google store and one for Firefox.

Jim

amancandance said:

I've always used 3rd party anti-virus and firewall software, but it looks like windows finally offers an in-built package that means I no longer need to buy a security service. Is this advisable?

In Windows 10 I've never used anything else except the built in Windows Defender (now re-branded as Windows Security). I've never had any problems or infections. It can be made even more effective by enabling potentially unwanted program/application (PUP/PUA) detection.

Enable or Disable Windows Defender PUA Protection in Windows 10

Windows security is all that I use too. I will scan occasionally with Malware bytes and it never finds anything anymore.

amancandance said:

I've always used 3rd party anti-virus and firewall software, but it looks like windows finally offers an in-built package that means I no longer need to buy a security service. Is this advisable? I have a Kaspersky subscription and I read that they can co-exist, but removing software is always preferable if it's unnecessary. What do you think?

If you decide not to use Kasperky, or your subscription runs out, Windows Defender is just fine. Check out this post in a similar thread: Is Windows Security okay or no?