Fresh install of LO 18.104.22.168 and JDK 1.8.0_111 (as JRE is not detected for me; may be related to https://bugs.documentfoundation.org/show_bug.cgi?id=103507) on OSX Sierra 10.12.
I've tried installing Zotero extension as well as LanguageTool3.5. Opening the .oxt file causes LibreOffice to freeze and start trashing memory.
Steps to Reproduce:
1. Upgrade to JDK 1.8.0_111 and select in LibreOffice
2. Try installing an extension like Language Tool http://extensions.libreoffice.org/extension-center/languagetool
LibreOffice freezes and trashes memory until killed
An extension is installed
User Profile Reset: No
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.71 Safari/537.36
*** This bug has been marked as a duplicate of bug 99784 ***