This does not work in Firefox.

Power down the VM

Then right-click on the VM and select Edit Settings...
Select the VM Options tab.
Click on Advanced.
Scroll down to Configuration Parameters and click on EDIT CONFIGURATION...

Then click on ADD CONFIGURATION PARAMS for each parameter you want to add.

Fix keyboard key repeat:
NAME							VALUE
keyboard.typematicMinDelay		2000000

Enable cut/paste of text between host and guest.
NAME							VALUE
isolation.tools.copy.disable	false
isolation.tools.paste.disable	false