This question is asked SO MANY TIMES!!!
MSE could care less, lost its certificate. AVG is crap.
It all depends on your computer environment. Bitdefender Free works for me. It's light weight, cloud based and you don't even know it's there. If it finds a site is infected it will block you from going there, but show a link to reload the page and enter anyway at your risk. Sometimes this could be a false positive.
I use an addon in Firefox, Palemoon and Cyberfox called Noscript. This is like a gate before your anti-virus. If you use it allow base 2nd level domains in the options to be less cumbersome.
I also use Sandboxie. This will launch your browser in a virtual environment and so malware can't touch your computer. In Sandboxie's settings configure to delete contents on exit, allow access to bookmarks and the profile at reduced security, but less cumbersomeness.
If you do use Avast and have certain addons in Firefox Avast will remove them. Total crap! I have had nothing but problems with Avast.
Not all anti-virus programs are 100% efficient.