I have previously posted an entry on the latest version of Firefox 19.0.2 where I mentioned that there were speed problems accessing certain web sites, including but not restricted to the BBC web sites.
The following article was posted the other day which may go some way to explaining my observations. Access to the article may be slow, but it describes how a row between a spam-fighting group (Spamhaus) and hosting firm (Cyberbunker) has sparked retaliation attacks affecting the wider internet.