Thanks Johannes for the comprehensive answer. Alleviates my concern that my browser or virus blocker may have been responsible.
One last comment -- you said that you prefer to have images embedded as thumbnails, but in my Chrome browser, all I see in some posts is a notice that attachment is blocked, followed by a link, not a thumbnail (which would be much better).
At any rate, I'm a new member, so appreciate your tolerating my ignorance. A wonderful web site.