I was having problems accessing the IBM documentation from my Firefox browser. Nothing was displayed. The Firefox error log reported problems with some of the HTML. I started getting problems with other sites, such as being unable to logon to gmail. I was getting annoyed with all of these little problems, so I decided to find out why.
I eventually fixed the problems by refreshing Firefox. Type about:support on the input line, and click the box saying “Refresh Firefox”. After a few moments it came back and worked.
I can access all sites, including the IBM documentation.
I only regret clearing my cache beforehand!