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

Here are the details from the Slackware 14.2 ChangeLog:
+--------------------------+
patches/packages/mozilla-thunderbird-52.5.2-i586-1_slack14.2.txz: Upgraded.
This release contains security fixes and improvements.
For more information, see:
https://www.mozilla.org/en-US/thunderbird/52.5.2/releasenotes/
(* 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-52.5.2-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-52.5.2-x86_64-1_slack14.2.txz

Updated package for Slackware -current:
ftp://ftp.slackware.com/pub/slackware/slackware-current/slackware/xap/mozilla-thunderbird-52.5.2-i586-1.txz

Updated package for Slackware x86_64 -current:
ftp://ftp.slackware.com/pub/slackware/slackware64-current/slackware64/xap/mozilla-thunderbird-52.5.2-x86_64-1.txz


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

Slackware 14.2 package:
3aaa346a9ce9776f861aaedc15b7ae40 mozilla-thunderbird-52.5.2-i586-1_slack14.2.txz

Slackware x86_64 14.2 package:
e649a1416aa4bebb06a25420fc039dd4 mozilla-thunderbird-52.5.2-x86_64-1_slack14.2.txz

Slackware -current package:
0812aaf27ccc167a289ee32dd16d7966 xap/mozilla-thunderbird-52.5.2-i586-1.txz

Slackware x86_64 -current package:
e0fc69361d618894ecec6958fef1c974 xap/mozilla-thunderbird-52.5.2-x86_64-1.txz


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

Upgrade the package as root:
# upgradepkg mozilla-thunderbird-52.5.2-i586-1_slack14.2.txz

  Mozilla-Thunderbird (SSA:2017-356-01) Update for Slackware