Tainted Bookmarks

Here is a question for any computer gurus on board.

I noticed yesterday that some of the bookmarks in Mozilla Firefox don't work. I get an error message saying "access refused". I tried the same bookmarks using IE "Favorites", and got a "The page cannot be displayed" message. Also noticed that when using Google, some of sites listed "could not be found".

These sites all seem to have what someone might consider questionable material - nudity, references to sex, violence, "drugs" etc, but not necessarily porn. Kinda like the filter we have on our computers at work.

Interestingly, on one of the sites I was able to work around the blocking by accessing it via a link from another page. I bookmarked it again, and the bookmark works fine. The original bookmark still wouldn't work, but checking "properties" showed the two to be identical.

I tried copying and pasting the URL from the top of the web page. It worked fine when copied from the successful download, but when I copied and pasted from the page with the error message, it wouldn't load.

Has anyone else experienced anything like this? I use Charter high speed cable internet service, and wondering if the ISP has quietly slipped in a filter against what someone might consider objectionable material.

Not that I spend appreciable time surfing porn (an excellent way to pick up viruses, trojans and spyware), but I do object to someone else deciding what I should be able to download. Besides, some of the refused sites are completely "legitimate."

Any suggestions to what is going on?