Sandbox Tor Browser no longer starting (100% CPU load)

Sandbox Tor Browser no longer working after update to Tor Browser 7.5a3. (Also happens with a fresh install.)

tor-browser-sandboxed shows that everything is ok:

...
2017/07/28 19:33:11 sandbox: bwrap pid is: 298684
2017/07/28 19:33:11 sandbox: bwrap init pid is: 298685
2017/07/28 19:33:11 launch: Complete.
2017/07/28 19:33:11 update: Previous scheduled update check: 2017-07-28 21:15:25 +0200 CEST
2017/07/28 19:33:11 update: Initial scheduled update check: 1h42m13.489734672s

But the firefox process uses 100% CPU and appears to be stuck in an endless loop:

$ strace -p 298688
read(-2, 0x7ffcbab09010, 32)            = -1 EBADF (Bad file descriptor)
read(-2, 0x7ffcbab09010, 32)            = -1 EBADF (Bad file descriptor)
...
read(-2, 0x7ffcbab09010, 32)            = -1 EBADF (Bad file descriptor)
read(-2, 0x7ffcbab09010, 32)            = -1 EBADF (Bad file descriptor)

$ sandboxed-tor-browser -version
sandboxed-tor-browser 0.0.12-dev (26c9478)

$ lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 9.1 (stretch)
Release:        9.1
Codename:       stretch

Trac:
Username: pege