LibreOffice 5.3 will be announced at the end of January 2017, with a large number of new features which are summarized on the release notes page: https://wiki.documentfoundation.org/ReleaseNotes/5.3. In order to find, report and triage bugs, the QA team is organizing a third bug hunting session on Friday, December 9, and Saturday, December 10, 2016.
Tests will be performed on LibreOffice 5.3 Beta 2, which will be available on the pre-releases server (http://dev-builds.libreoffice.org/pre-releases/) in time for the event. Builds will be available for Linux (DEB and RPM), MacOS and Windows, and will run in parallel with the production version.
Mentors will be available on December 9 and December 10, 2016, from 8AM UTC to 10PM UTC. Of course, hunting bugs will be possible also on other days, as the builds of LibreOffice 5.3.0 Beta 2 will be available until mid December.
During the dedicated sessions, we will concentrate all efforts to chase and reproduce the bugs, in order to confirm and file them in a more comprehensive way. Of course, the more comprehensive the bug report, the easier it will be for the developers to solve the bugs in time for the final release.