When I click on "Help>Online Help" I get an error message "No HTML Browser Found. Please define one in "Tools>Options>Help>Help Options". When I do so, I get a dialog where I entered "C:\Program Files (x86)\Mozilla Firefox" where is located "firefox.exe".
I finally figured out that I had to enter "C:\Program Files (x86)\Mozilla Firefox\firefox.exe" in the browser path, and now it works. It opens a tab with "file:///C:/lazarus//docs/index.html".
I would really like to have access to the help files from Borland Delphi which are located in "C:\Program Files (x86)\Borland\Delphi4\Help". They are ".hlp" files but my system is configured to open them.