They're lined up in hospital firm briefly in county (9)
I believe the answer is:
bedsteads
'they're lined up in hospital' is the definition.
(as in a line of beds on a hospital ward)
'firm briefly in county' is the wordplay.
'firm' becomes 'steady' (similar in meaning).
'briefly' means to remove the last letter.
'in' indicates putting letters inside.
'county' becomes 'beds' (abbreviation for Bedfordshire).
'steady' with its final letter taken away is 'stead'.
'stead' put within 'beds' is 'BEDSTEADS'.
(Another definition for bedsteads that I've seen is " Frameworks supporting springs and mattresses".)