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-60.5.1-i686-1_slack14.2.txz: Upgraded.
This release contains security fixes and improvements.
For more information, see:
https://www.mozilla.org/en-US/thunderbird/60.5.1/releasenotes/
https://www.mozilla.org/security/known-vulnerabilities/thunderbird.html
https://www.mozilla.org/en-US/security/advisories/mfsa2019-06/
https://www.mozilla.org/en-US/security/advisories/mfsa2019-06/#CVE-2018-18356
https://www.mozilla.org/en-US/security/advisories/mfsa2019-06/#CVE-2019-5785
https://www.mozilla.org/en-US/security/advisories/mfsa2019-06/#CVE-2018-18335
https://www.mozilla.org/en-US/security/advisories/mfsa2019-06/#CVE-2018-18509
(* 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-60.5.1-i686-1_slack14.2.txz

Updated package for Slackware x86_64 14.2:
ftp://ftp.slackware.com/pub/slackware/slackware64-14.2/patches/packages/mozilla-thunderbird-60.5.1-x86_64-1_slack14.2.txz

Updated package for Slackware -current:
ftp://ftp.slackware.com/pub/slackware/slackware-current/slackware/xap/mozilla-thunderbird-60.5.1-i686-1.txz

Updated package for Slackware x86_64 -current:
ftp://ftp.slackware.com/pub/slackware/slackware64-current/slackware64/xap/mozilla-thunderbird-60.5.1-x86_64-1.txz


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

Slackware 14.2 package:
3e8873418e8d296bdf92fe714b5cec98 mozilla-thunderbird-60.5.1-i686-1_slack14.2.txz

Slackware x86_64 14.2 package:
f8cc5973632938ef4909194d28614161 mozilla-thunderbird-60.5.1-x86_64-1_slack14.2.txz

Slackware -current package:
be4adb59748d0fa1e6f0b9ee518fd935 xap/mozilla-thunderbird-60.5.1-i686-1.txz

Slackware x86_64 -current package:
8549bb7d564e205a4ec931dc02a52d9f xap/mozilla-thunderbird-60.5.1-x86_64-1.txz


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

Upgrade the package as root:
# upgradepkg mozilla-thunderbird-60.5.1-i686-1_slack14.2.txz

  Mozilla-Thunderbird (SSA:2019-045-01) Update for Slackware