I check off all the options in xfce4-accessibility-settings, but it's still messing up. When I hold shift for 8-10 seconds, slow keys enable. When I press shift 5 times in a row sticky keys enable. I just can't disable it forever! The only solution I found is to run gnome-at-properties and close the window appeared. Just start and exit. It resets keyboard settings like compose key, group change combination and so on but it also shut off these annoying accessibility functions. After restarting Xorg they are enabled again.

Strangely, I've found a lot of solutions for GNOME and KDE (all the same) but not a single solution for XFCE.

If this is not a bug I only ask for the command-line solution of disabling this. Some setxkbmap options or so, because gnomes configurator somehow does this so I guess it may be done via some scripting.