In Chrome today (and perhaps earlier) when I attempt to add an answer to a StackOverflow question, I find no row of buttons above the entry box and so cannot easily add links or font styles. If I log in with IE, no problem. [Windows 7/64]
All the evidence points to this having been a cache issue. It is not possible to confirm this because the problem no longer occurs.
Please do not again delete my answer to my own (implied) question. The fact that I have accepted the strong probability that it was a cache issue may be of value to others who research a similar problem.