This happens as you are typing? That should not be. Does this happen everywhere, some sites, a few?

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

Type about:support in the address bar and press Enter. Under the main banner, press the button; Copy Text To Clipboard.. Then in the reply box at the bottom of this page, do a right click in the box and select Paste. This will show us your system details. No Personal Information Is Collected.

Keyconfig should be available for Firefox 39 AFAIK.

I don't think that there is a way to disable a page down with Space or a page up with Shift+Space. I've seen such request in the past and I can't remember doing this reliably like with a Greasemonkey script.

You shouldn't have a scroll action if you type in a text area.

Do you mean that you can't type a space on some web pages?

cor-el,

"Not available message displayed" for KeyConfig @ https://addons.mozilla.org/en-US/firefox/addon/functions-for-keyconfig/

Tried to download and install anyway and received another incompatibility message.

Currently, I cannot type a space at the command prompts for the one training site. The space bar functions as it should at other sites. I realize it is probably a site issue, but a workaround would be very helpful.

There are a number of similarly named keyconfig extensions...

The one I used in the old days is here: http://mozilla.dorando.at/

Support thread here seems to be active: http://forums.mozillazine.org/viewtopic.php?f=48&t=72994