Is it just Firefox 15.0.1 being strange or is their something in your web pages which makes it hard to mark a piece of text. It unmarks itself as soon as you release the left mouse button. I have the NoScript and AdBlock plus extensions disabled on semiaccurate.
I had a heck of a time copying enough info to start a forum thread on your article about M$ losing server market share. You've been sneaky, haven't you :-)