how to install offline help 6.3 (ubuntu 19.10)?

ubuntu 19.10 Libreoffice Version:
Build ID: 1:6.3.5-0ubuntu0.19.10.1
CPU threads: 4; OS: Linux 5.3; UI render: default; VCL: gtk3;
Locale: en-US (en_US.UTF-8); UI-Language: en-US
Calc: threaded

I installed english-office-help-english-us but when I select ‘Help - Libreoffice help’ (F1) I get this url displayed in Firefox and a blank screen;


a list of /usr/share/libreoffice/help/;


a11y-toggle.js help2.js idxcaption.xsl main_transform.xsl polyfills.js
default.css help.html idxcontent.xsl media prism.css
en-US help.js index.html normalize.css prism.js
fuzzysort.js hid2file.js languages.js paginathing.js

Is it a bug?

Make sure you have JavaScript enabled in your browser.

Thanks… .