keep your twitter passphrase in vault, use a dispvm.
if your low on resources and want to make a dedicated vm that will be used for twitter and other things, you could use firejail --home, and maybe --x11 as well for isolation. for this to be effective, you'll also need to add "-nolisten local" to your templates qubes-run-xorg.sh https://firejail.wordpress.com
another isolation you can use is firefox containers, which are not enforced sandboxes, but more of a privacy and organizational separation. this feature is in testing. https://testpilot.firefox.com/experiments/containers/
the two work fine together if you want to use them both. if have the resources, i think its better to use a dispvm or dedicated twittervm.
to clarify, "-nolisten local" should go in the last line, so it should read
exec su -l user -c "/usr/bin/xinit $XSESSION -- $XORG :0 -nolisten local -nolisten tcp vt07 -wr -config xorg-qubes.conf > ~/.xsession-errors 2>&1"