I'm seeing something very similar as well.  Every time I try to open/close/delete a message in Thunderbird, DBUS take up ~100% CPU and thunderbird takes up about the other 100% of my other CPU for about 10-15 seconds.

Number of files total and per process looks similar to when it isn't happening.

Restarted didn't seem to make any difference.

I see a massive plethora of the following with strace -p

recvmsg(24, {msg_name(0)=NULL, msg_iov(1)=[{"a11y.atspi.Component\0\0\0\0\0\0\0\0\0\0\0\0"..., 2048}], msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 2048
recvmsg(24, {msg_name(0)=NULL, msg_iov(1)=[{"e\0\0\0\30\0\0\0org.a11y.atspi.Component"..., 2048}], msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 2048
poll([{fd=4, events=POLLIN}, {fd=3, events=POLLIN}, {fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=9, events=POLLIN}, {fd=8, events=POLLIN}, {fd=10, events=POLLIN}, {fd=11, events=POLLIN}, {fd=12, events=POLLIN}, {fd=13, events=POLLIN}, {fd=15, events=POLLIN}, {fd=16, events=POLLIN}, {fd=17, events=POLLIN}, {fd=18, events=POLLIN}, {fd=19, events=POLLIN}, {fd=20, events=POLLIN}, {fd=21, events=POLLIN}, {fd=14, events=POLLIN}, {fd=22, events=POLLIN}, {fd=23, events=POLLIN}, {fd=25, events=POLLIN}, {fd=26, events=POLLIN}, {fd=27, events=POLLIN}, {fd=24, events=POLLIN}, {fd=28, events=POLLIN}, {fd=29, events=POLLIN}], 26, 108294) = 1 ([{fd=24, revents=POLLIN}])
recvmsg(24, {msg_name(0)=NULL, msg_iov(1)=[{"52867\0\0\0\0\0\0\0=\0\0\0\31\0\0\0org.a11y.ats"..., 2048}], msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 2048
recvmsg(24, {msg_name(0)=NULL, msg_iov(1)=[{"7\0\0\0!\0\0\0/org/a11y/atspi/accessib"..., 2048}], msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 2048
poll([{fd=4, events=POLLIN}, {fd=3, events=POLLIN}, {fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=9, events=POLLIN}, {fd=8, events=POLLIN}, {fd=10, events=POLLIN}, {fd=11, events=POLLIN}, {fd=12, events=POLLIN}, {fd=13, events=POLLIN}, {fd=15, events=POLLIN}, {fd=16, events=POLLIN}, {fd=17, events=POLLIN}, {fd=18, events=POLLIN}, {fd=19, events=POLLIN}, {fd=20, events=POLLIN}, {fd=21, events=POLLIN}, {fd=14, events=POLLIN}, {fd=22, events=POLLIN}, {fd=23, events=POLLIN}, {fd=25, events=POLLIN}, {fd=26, events=POLLIN}, {fd=27, events=POLLIN}, {fd=24, events=POLLIN}, {fd=28, events=POLLIN}, {fd=29, events=POLLIN}], 26, 108293) = 1 ([{fd=24, revents=POLLIN}])
recvmsg(24, {msg_name(0)=NULL, msg_iov(1)=[{"\37\0\0\0/org/a11y/atspi/accessible/r"..., 2048}], msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 2048
recvmsg(24, {msg_name(0)=NULL, msg_iov(1)=[{"/a11y/atspi/accessible/672136\0\0\0"..., 2048}], msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 2048
poll([{fd=4, events=POLLIN}, {fd=3, events=POLLIN}, {fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=9, events=POLLIN}, {fd=8, events=POLLIN}, {fd=10, events=POLLIN}, {fd=11, events=POLLIN}, {fd=12, events=POLLIN}, {fd=13, events=POLLIN}, {fd=15, events=POLLIN}, {fd=16, events=POLLIN}, {fd=17, events=POLLIN}, {fd=18, events=POLLIN}, {fd=19, events=POLLIN}, {fd=20, events=POLLIN}, {fd=21, events=POLLIN}, {fd=14, events=POLLIN}, {fd=22, events=POLLIN}, {fd=23, events=POLLIN}, {fd=25, events=POLLIN}, {fd=26, events=POLLIN}, {fd=27, events=POLLIN}, {fd=24, events=POLLIN}, {fd=28, events=POLLIN}, {fd=29, events=POLLIN}], 26, 108292) = 1 ([{fd=24, revents=POLLIN}])
recvmsg(24, {msg_name(0)=NULL, msg_iov(1)=[{"o)a(so)assusau)\0\5\0\0\0:1.27\0\0\0!\0\0\0"..., 2048}], msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 2048
recvmsg(24, {msg_name(0)=NULL, msg_iov(1)=[{"AddAccessible\0\0\0\10\1g\0\32((so)(so)(s"..., 2048}], msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 2048