You can execute a global command to close all folds of block comments:
:g/^\/\*/foldc
:help foldclose , /* ( ). , / * . /, (, :g#^/\*#foldc). , , . :
set fdm=syntax fen
augroup closeCommentFolds
au!
au FileType javascript %foldo | g/^\/\*/foldc
au FileType ruby %foldo | g/^=begin/foldc
augroup end
, ^ regex , /* =begin . , ^\s* ^. %foldo , foldenable, ( ).