Random BSODs frequently...please help..

I'm seeing a recurrent theme of memory management/memory corruption from what you've provided.
You should probably go ahead and check it by running memtest overnight. (needs to run for several passes and will take some time so I suggest overnight)
See link for tutorial on using memtest - RAM - Test with Memtest86+

Code:

Probably caused by : memory_corruption ( nt!MiBadShareCount+4c )

Followup: MachineOwner
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2: kd> !analyze -v
*******************************************************************************
*                                                                             *
*                        Bugcheck Analysis                                    *
*                                                                             *
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PFN_LIST_CORRUPT (4e)
Typically caused by drivers passing bad memory descriptor lists (ie: calling
MmUnlockPages twice with the same list, etc).  If a kernel debugger is
available get the stack trace.
Arguments:
Arg1: 0000000000000099, A PTE or PFN is corrupt
Arg2: 00000000000506eb, page frame number
Arg3: 0000000000000002, current page state
Arg4: 00000000000506ea, 0

Debugging Details:
------------------


BUGCHECK_STR:  0x4E_99

CUSTOMER_CRASH_COUNT:  1

DEFAULT_BUCKET_ID:  VISTA_DRIVER_FAULT

PROCESS_NAME:  firefox.exe

CURRENT_IRQL:  2

LAST_CONTROL_TRANSFER:  from fffff8000311c32c to fffff8000308df00

STACK_TEXT:  
fffff880`04755e08 fffff800`0311c32c : 00000000`0000004e 00000000`00000099 00000000`000506eb 00000000`00000002 : nt!KeBugCheckEx
fffff880`04755e10 fffff800`0302534c : c8000000`506eb863 fffffa80`00f14c10 00000000`00000000 000001d0`00000004 : nt!MiBadShareCount+0x4c
fffff880`04755e50 fffff800`03083585 : 00000000`00000000 00000000`00000111 00000000`00000000 00000000`00000000 : nt! ?? ::FNODOBFM::`string'+0x47aa7
fffff880`04755fb0 fffff800`031bd34f : fffff900`c2aef630 00000000`00000000 fffffa80`05d8f3f0 fffff880`03c41000 : nt!MiFreePagedPoolPages+0x129
fffff880`04756100 fffff800`031c187c : 00000000`00000000 fffff880`047562d0 fffff880`04756240 00000000`00000001 : nt!MiFreePoolPages+0x343
fffff880`04756210 fffff960`000c4ad8 : fffff900`c3a00228 fffff880`04756310 00000000`35316847 00000000`00000001 : nt!ExFreePoolWithTag+0x7cc
fffff880`047562c0 fffff960`000c52b2 : fffff900`c00bf010 fffff900`c3a00000 00000000`00000000 fffff900`c3a00228 : win32k!FreeObject+0x58
fffff880`047562f0 fffff960`000c544c : ffffffff`00000000 fffff880`00000000 fffff900`c3a00000 fffff900`00000000 : win32k!SURFACE::bDeleteSurface+0x58a
fffff880`04756440 fffff960`0008661d : ffffffff`d1051304 fffff900`c3a00000 00000000`00001304 00000000`7efdb000 : win32k!bDeleteSurface+0x34
fffff880`04756470 fffff800`0308d153 : fffffa80`0427a800 fffff880`04756520 00000000`038f0820 fffff900`c00bf010 : win32k!NtGdiDeleteObjectApp+0xd5
fffff880`047564a0 00000000`74a72dd9 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : nt!KiSystemServiceCopyEnd+0x13
00000000`0014d078 00000000`00000000 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : 0x74a72dd9

well if the memory is actually bad it could just mean you use firefox a lot.
that's why I just jump straight to the test it's free and can run while you sleep.
then we know.

I'm currently not of the mind that it will be the case.

If firefox is the ONLY thing that is crashing which is not what I saw, it could be the nvidia firefox problem. Which apparently exists even though it hasn't hit me on either of my nvidia machines.
For that you just have to turn off hardware acceleration in firefox. in options under the advanced tab. Note that firefox will take a noticeable performance hit when this is done.