|Hosts is easy to check. Just follow this path:|
The file is simply named Hosts without an extension. If you see more than one then you will need untick "hide file extensions for known file types" (Control Panel > Folder Options >View).
The Hosts file can be opened with NotePad. If you just want to elimate it from the equation then just simply rename it from Hosts to Hosts.txt and it will be disabled.
I don't think you have to reboot but it wouldn't hurt just to be sure. Afterwards you can remove the ".txt" bit again.
Restricted sites can be found in IE:
Tools > Internet Options > Security > Restricted Sites icon > Sites button. The difficulty is knowing what should or should not be listed. If you are using something like SpywareBlaster there will be a gigantic list to wade through, making it about impracticable to do.
If you don't know about advert blocking then it is about certain that you will not have anything like that in IE (you have to make deliberate steps and it is only recently that anything really suitable has come along).
It is possible that an advert blocker has installed in Firefox. To check this go to Tools > Add-ons > Extensions - you will see "AdBlock Plus". This can be temporarily disabled, if present, but I am running it and don't seem to have all of the issues that you are getting.
As for Malware etc, well I have to admit that if the only symptoms you are getting are to do with those particular websites then it is probably unlikely. Usually machines with Malware exhibit other symptoms, often rendering them unreliable. I assume you have some sort of virus checker on board. Whether you have or not you could download the free version of MalwareBytes, install it, update it and Run it. It is small program that you don't normally need to run in the background, so it is worth keeping onboard and updated from time to time (just in case you are ever unlucky).
See how you get on. I have a few more ideas but they are diminishing fast - all rather weird.
How to know you are getting old 5:
A lamp post backs into you