Safari crashes constantly- Crashed Thread: 6 JavaScriptCore::Marking

Question

This has been happening for a while and crash reports are always the same. :  Crashed Thread:  6  JavaScriptCore::Marking
I've used Apple Hardware Test and Rember to test if it's a RAM issue, but both come up fine and don't detect anything.
Below is the latest truncated report. I'll post the full one if necessary.
Process:         WebProcess [870]
Path:            /System/Library/StagedFrameworks/Safari/WebKit2.framework/WebProcess.app/Conten ts/MacOS/WebProcess
Identifier:      com.apple.WebProcess
Version:         8537 (8537.73.11)
Build Info:      WebKit2-7537073011000000~3
Code Type:       X86-64 (Native)
Parent Process:  ??? [780]
User ID:         501
Date/Time:       2014-02-12 11:10:20.863 -0500
OS Version:      Mac OS X 10.8.5 (12F45)
Report Version:  10
Interval Since Last Report:          393622 sec
Crashes Since Last Report:           3
Per-App Interval Since Last Report:  134969 sec
Per-App Crashes Since Last Report:   1
Anonymous UUID:                      63079B78-60B2-A08F-2673-81DFC5AB9A8D
Crashed Thread:  6  JavaScriptCore::Marking
Thread 6 Crashed:: JavaScriptCore::Marking
0   com.apple.JavaScriptCore                0x0000000106793bda JSC::CodeBlock::updateAllPredictionsAndCountLiveness(JSC::OperationInProgress, unsigned int&, unsigned int&) + 154
1   com.apple.JavaScriptCore                0x000000010689b315 JSC::CodeBlock::stronglyVisitStrongReferences(JSC::SlotVisitor&) + 1317
2   com.apple.JavaScriptCore                0x000000010689abee JSC::CodeBlock::visitAggregate(JSC::SlotVisitor&) + 382
3   com.apple.JavaScriptCore                0x000000010689ad4f JSC::FunctionExecutable::visitChildren(JSC::JSCell*, JSC::SlotVisitor&) + 159
4   com.apple.JavaScriptCore                0x000000010671918d JSC::SlotVisitor::drain() + 541
5   com.apple.JavaScriptCore                0x0000000106718d27 JSC::SlotVisitor::drainFromShared(JSC::SlotVisitor::SharedDrainMode) + 343
6   com.apple.JavaScriptCore                0x00000001066fb67a JSC::GCThread::gcThreadMain() + 74
7   com.apple.JavaScriptCore                0x00000001066f05ef ***::wtfThreadEntryPoint(void*) + 15
8   libsystem_c.dylib                       0x00007fff8a523772 _pthread_start + 327
9   libsystem_c.dylib                       0x00007fff8a5101a1 thread_start + 13

Answer 1

That kind of crash is usually, or perhaps always, caused by a hardware fault.
If your model has user-replaceable memory, and you've upgraded the memory modules, reinstall the original memory and see whether there's any improvement. Be careful not to touch the gold contacts. Clean them with a mild solvent such as rubbing alcohol. Aftermarket memory must exactly match the technical specifications for your model. Memory that is either slower or faster than specified may be incompatible.
Apple Diagnostics or the Apple Hardware Test, though generally unreliable, will sometimes detect a fault. A negative test can't be depended on. Run the extended version of the test, if applicable.