What in bejeebuz has happened to text editing in my web browser?

So, at some point, it seems in the last few weeks, I noticed a terribly frustrating problem with trying to enter messages in Facebook using my Firefox web browser on Windows 7. And today, I’m seeing the same sort of problem on the Reddit web site.

The problem is the text editor windows (on those sites, but not on Fluther) does awful things such as:

* Lose focus when I hit Enter (Facebook has been doing this for even longer).

* Make it look like I can cut & paste in a message with line breaks (paragraphs), but then (either before or after I save it) ignore/remove all the line breaks and post it as one huge paragraph.

* When I try to cut & paste within the post, remove huge unselected sections.

* Cut & paste the wrong sections.

* Other chaotic nonsense.

Has anyone else run into this and does anyone know of a fix?