Hm. did you try to
a) completely close your broser
b) remove your browser's cache & configuration
before reinstalling?

I am a little unsure how a threat could have escaped your browser and infected the operating system itself.
Keep in mind that clamav reports possible threats.

In the future, use the noscript addon, or uBlock origin in expert mode, disallowing all javascript by default!
I always do that and while I still don't like visiting dodgy sites, it is much safer this way.

There's a second part to your report I did not fully understand; maybe there's a DNS problem, too. That could also reside inside your browser (which browser btw?), but also outside of it, wherever your system does name resolution.
Or maybe even the router.