Doesn't look familiar. Was it a one off or repeatable?
I've got it 4 times since first January 2021.
But i could not indentify in which conditions it happens
Today, I updated ff to the latest build and got again a trap.
 Exception Report - created 2021/02/06 13:44:36
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 OS2/eCS Version:  2.45
 # of Processors:  4
 Physical Memory:  3470 mb
 Virt Addr Limit:  2816 mb
 Exceptq Version:  7.11.3-shl (Jul  5 2016)
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 Exception C0000005 - Access Violation
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 Process:  W:\PROGRAMS\FIREFOX\FIREFOX.EXE (11/11/2020 21:59:20 74,241)
 PID:      6C (108)
 TID:      01 (1)
 Priority: 200
 Filename: W:\PROGRAMS\FIREFOX\XUL.DLL (11/11/2020 22:08:01 41,073,853)
 Address:  005B:AB848BAA (0001:02C38BAA)
 Cause:    Attempted to read from 00000010
           (not a valid address)
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 Failing Instruction
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 AB848B9A  TEST EBP, EBP         (85ed)
 AB848B9C  JZ   0xab848ce8       (0f84 46010000)
 AB848BA2  MOV  [ESP], EBP       (892c24)
 AB848BA5  CALL 0xab844da0       (e8 f6c1ffff)
 AB848BAA >MOV  EAX, [EAX+0x10]  (8b40 10)
 AB848BAD  MOV  EAX, [EAX+0x20]  (8b40 20)
 AB848BB0  MOV  ECX, [EAX+0x10]  (8b48 10)
 AB848BB3  TEST ECX, ECX         (85c9)
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 Registers
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 EAX : 00000000   EBX  : 0013C87C   ECX : 20F33E0C   EDX  : AB5B8B84
 ESI : 2DEC3300   EDI  : 0013C7EC
 ESP : 0013C7C0   EBP  : 20F33D20   EIP : AB848BAA   EFLG : 00210206
 CS  : 005B       CSLIM: FFFFFFFF   SS  : 0053       SSLIM: FFFFFFFF
 EAX : not a valid address
 EBX : read/write memory on this thread's stack
 ECX : read/write memory allocated by LIBCN0
 EDX : read/exec  memory at 0001:029B0B84 in XUL
 ESI : read/write memory allocated by LIBCN0
 EDI : read/write memory on this thread's stack
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 Stack Info for Thread 01
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   Size       Base        ESP         Max         Top
 00100000   00140000 -> 0013C7C0 -> 00114000 -> 00040000
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 Call Stack
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   EBP     Address    Module     Obj:Offset    Nearest Public Symbol
 --------  ---------  --------  -------------  -----------------------
 Trap  ->  AB848BAA   XUL       0001:02C38BAA  between nsDocShell::GetOriginAttributes + 4A and nsDocShell::CreatePrincipalFromReferrer - 166  (both in Unified_cpp_docshell_base0.cpp)
 20F33D20  AB85A21C   XUL       0001:02C4A21C  between nsDocShell::{vtable} + 534 and nsQueryObject::{vtable} - 6E0  (both in Unified_cpp_docshell_base0.cpp)
 AB859CF0  AB83F740   XUL       0001:02C2F740  nsDocShell::AddRef  (in Unified_cpp_docshell_base0.cpp)
 Lost Stack chain - new EBP below previous
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