sp_BlitzFirst: blocking_session_id not displayed in list of session_ids I have version sp_BlitzFirst 2016-12-10.

I executed the following:

sp_blitzfirst @ExpertMode = 1, @CheckProcedureCache = 1, @OutputType = 'Opserver1'

Below output shows SPID 124 is blocked by SPID 143, however SPID 143 did not show up in any of the output.  Is there another way to have sp_BlitzFirst show the info of the blocking_sesesion_id as well, so I can see what query is being executed?
It's most likely that the blocking SPID is sleeping. If you run sp_BlitzFirst again, look in the second section down, and you may see warnings for sleeping sessions with open transactions. 

By default sp_BlitzWho filters out sleeping SPIDs. We did recently add a parameter to show them, but we haven't bubbled it up to sp_BlitzFirst yet. 

I'm on my phone so I can't post screen caps at the moment. Leave a comment if you need more information. 

Thanks!