I know this is an old thread but this just started happening to me a few days ago and it's making me crazy so I'm going to try to revive it. I see no solutions when I search on it - the link given in this thread only goes to a Messenger download page - it seems Messenger is working fairly normal. It only happens on Facebook. In Chrome whenever I start to type it jumps to the post below, but I also tested in Firefox and MS Edge. It does the same thing in MS Edge, and in Firefox I can't even input a letter. It doesn't happen when typing into any other web pages or working in other programs on my computer.

My system is a laptop (Lenovo IdeaPad Flex), with external monitor and external wireless Keyboard & Mouse combo (also Lenovo). These items are connect to my laptop with a Sabrent USB dock. These are items I have used for a very long time so likely not a result of using them.

The keyboard glitch happens both when using the external keyboard and the laptop keyboard. At first I thought maybe my keyboard batteries were low so I changed them out. Didn't fix anything. Then I thought that since I often eat at my computer maybe food got stuck. So I cleaned it with canned air duster, then wiped it down. Didn't fix anything. Next I thought I needed to get inside the keyboard to get it cleaner so I tried to take it apart but it didn't want to come apart no matter how many screws I took out. I even broke one of the 'feet' that make it sit at an angle in the process. It was after this that I tried to type using the onboard keyboard. It did exactly the same thing as the external one, so I wasted a lot of time and got a broken foot for all my efforts.

It seems clear to me that this is a Facebook problem that has returned and I reported it to them a couple days ago. Just hoping somebody, somewhere, somehow, sees this newer comment and has found a solution they can share with me. I doubt very much that Facebook will even read my feedback 'report'.