New mozilla-thunderbird packages are available for Slackware 14.2 and -current to fix security issues.

Here are the details from the Slackware 14.2 ChangeLog:
+--------------------------+
patches/packages/mozilla-thunderbird-52.9.0-i586-1_slack14.2.txz: Upgraded.
This release contains security fixes and improvements.
For more information, see:
https://www.mozilla.org/en-US/thunderbird/52.9.0/releasenotes/
https://www.mozilla.org/en-US/security/advisories/mfsa2018-18/
(* Security fix *)
+--------------------------+


Where to find the new packages:
+-----------------------------+

Thanks to the friendly folks at the OSU Open Source Lab
(http://osuosl.org) for donating FTP and rsync hosting
to the Slackware project!

Also see the "Get Slack" section on http://slackware.com for
additional mirror sites near you.

Updated package for Slackware 14.2:
ftp://ftp.slackware.com/pub/slackware/slackware-14.2/patches/packages/mozilla-thunderbird-52.9.0-i586-1_slack14.2.txz

Updated package for Slackware x86_64 14.2:
ftp://ftp.slackware.com/pub/slackware/slackware64-14.2/patches/packages/mozilla-thunderbird-52.9.0-x86_64-1_slack14.2.txz

Updated package for Slackware -current:
ftp://ftp.slackware.com/pub/slackware/slackware-current/slackware/xap/mozilla-thunderbird-52.9.0-i586-1.txz

Updated package for Slackware x86_64 -current:
ftp://ftp.slackware.com/pub/slackware/slackware64-current/slackware64/xap/mozilla-thunderbird-52.9.0-x86_64-1.txz


MD5 signatures:
+-------------+

Slackware 14.2 package:
7971ca186c1478a4bb814405fdc06dee mozilla-thunderbird-52.9.0-i586-1_slack14.2.txz

Slackware x86_64 14.2 package:
5fca6fb0587d019549e01fcde7f2e42d mozilla-thunderbird-52.9.0-x86_64-1_slack14.2.txz

Slackware -current package:
724652a660f8639d1df2b07f4fceb5b3 xap/mozilla-thunderbird-52.9.0-i586-1.txz

Slackware x86_64 -current package:
10c7e523e93614e861a13501d9252534 xap/mozilla-thunderbird-52.9.0-x86_64-1.txz


Installation instructions:
+------------------------+

Upgrade the package as root:
# upgradepkg mozilla-thunderbird-52.9.0-i586-1_slack14.2.txz


+-----+

Slackware Linux Security Team
http://slackware.com/gpg-key
security@slackware.com

  Mozilla-Thunderbird Update (SSA:2018-186-01) for Slackware