That is a strange problem. Are there any simple forms where the space bar works, such as the ones on this site, or the search box on Wikipedia? A little while ago a common commenting platform called OpenWeb that is used on multiple sites had a problem with spaces, but they fixed it. Here's one of those threads for reference in case your problem is in a similar context: https://support.mozilla.org/questions/1388487 Regarding the window resizing, does the Mac have any keyboard shortcut involving the space bar that would do that? For example, combined with the option/alt key or other modifier key? Sometimes Firefox may be confused about a modifier key being pressed. Jabbing the modifier key repeatedly may help Firefox get the message that isn't not pressed.