Because python:3.7 no longer has USE=threads (always force-enabled), the PYTHON_REQ_USE variable should be updated to include "threads(+)".
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=8f46152178859d54bbdf53266662746ff875d961 commit 8f46152178859d54bbdf53266662746ff875d961 Author: Thomas Deutschmann <whissi@gentoo.org> AuthorDate: 2018-09-30 01:43:24 +0000 Commit: Thomas Deutschmann <whissi@gentoo.org> CommitDate: 2018-09-30 01:43:24 +0000 mail-client/thunderbird: update PYTHON_REQ_USE for Python 3.7 Closes: https://bugs.gentoo.org/667326 Signed-off-by: Thomas Deutschmann <whissi@gentoo.org> Package-Manager: Portage-2.3.50, Repoman-2.3.11 mail-client/thunderbird/thunderbird-60.0-r2.ebuild | 2 +- mail-client/thunderbird/thunderbird-60.0-r3.ebuild | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=cea19ee6d465f4d9c27f8a9eb96fdbbf49e290b3 commit cea19ee6d465f4d9c27f8a9eb96fdbbf49e290b3 Author: Thomas Deutschmann <whissi@gentoo.org> AuthorDate: 2018-09-30 01:41:54 +0000 Commit: Thomas Deutschmann <whissi@gentoo.org> CommitDate: 2018-09-30 01:41:54 +0000 www-client/firefox: update PYTHON_REQ_USE for Python 3.7 Closes: https://bugs.gentoo.org/667326 Signed-off-by: Thomas Deutschmann <whissi@gentoo.org> Package-Manager: Portage-2.3.50, Repoman-2.3.11 www-client/firefox/firefox-60.2.0.ebuild | 2 +- www-client/firefox/firefox-60.2.1-r1.ebuild | 2 +- www-client/firefox/firefox-62.0-r1.ebuild | 2 +- www-client/firefox/firefox-62.0.2.ebuild | 2 +- 4 files changed, 4 insertions(+), 4 deletions(-)