Hiya Marion
Thomas Firth age 51, Turkish Baths, Castlereagh Street/ 2 Richardsons Yard,Buried 20 August 1902, Section K plot 154.
Jeanette Bonny Firth age 45,14 Eastgate,Buried 2 February 1907 Section K plot 154
Can't see anymore burials in that grave under the name Firth.
Gertrude Firth age 21 month,No 16 Court, Shambles Street, Buried 17 June 1881, Section M plot 387.
Lucy Firth age 5 months, No 16 Court,4 Shambles Street, Buried 4 August 1881. Section M plot 387.
Ann Firth age 30, Shambles Street,Buried 28 February 1883,Section M plot 387.
I can't see any other burials in that grave with the surname Firth.
There are a couple of Mary Firth burials between 1881 and 1883 I'll write them in then you can make your mind up if I had to guess I'd go for the 1883 burial because of the location to Shambles Street and she was buried 6 days before Ann.
Mary Firth age 12,40 Boundry Street, Measbro Dyke,Buried 29 May 1881, Section N plot 621.
Mary Firth age 17 hours, Pinfold Hill,Buried 22 February 1883, Section N plot 690.
Regards Carolanne