Personalization doesn't work in LibfeOffice Version 5 and 6. Categories and Mozilla themes are not available.
Go to Personalization and try to add a new theme
New themes are loaded from mozilla or from the predefined categories.
User Profile Reset: No
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:58.0) Gecko/20100101 Firefox/58.0
It should be fixed in next release 6.0.1 (or 5.4.6 for 5.4 branch)
*** This bug has been marked as a duplicate of bug 114731 ***