Freezing Firefox 10.0.0.4411 stack.

Intel Xeon W3540 @ 2.93GHz running 64-bit Windows 7 Enterprise with 6 GB RAM + Nvidia Quadro FX 1800 (driver 8.15.11.9038). Firefox 10.0.0.4411 using about 1.5 GB for 700+ tabs in 23+ windows. Of 43 threads, the firefox.exe stack using 25+% CPU and freezing the GUI:

xul.dll!?GetType@ContainerLayer@layers@mozilla@@UBE?AW4LayerType@Layer@23@XZ+0x133ba
xul.dll!?GetFontAt@gfxFontGroup@@UAEPAVgfxFont@@H@Z+0xb10
xul.dll!?GetType@ContainerLayer@layers@mozilla@@UBE?AW4LayerType@Layer@23@XZ+0x133ba
xul.dll!NS_CycleCollectorForget2_P+0x11c61
xul.dll!NS_CycleCollectorForget2_P+0x10c18
xul.dll!NS_CycleCollectorSuspect2_P+0x3ae
xul.dll!?GetFirstChild@ContainerLayer@layers@mozilla@@UAEPAVLayer@23@XZ+0x422e
xul.dll!?GetType@ContainerLayer@layers@mozilla@@UBE?AW4LayerType@Layer@23@XZ+0x157b5
xul.dll!?GetType@ContainerLayer@layers@mozilla@@UBE?AW4LayerType@Layer@23@XZ+0x157ce
xul.dll!NS_CycleCollectorForget2_P+0xb3a
xul.dll!?ParseFontLanguageOverride@gfxFontStyle@@SAIABVnsString@@@Z+0x590
xul.dll!?GetType@ContainerLayer@layers@mozilla@@UBE?AW4LayerType@Layer@23@XZ+0xe0f7
xul.dll!?GetUnderlineOffset@gfxFontGroup@@UAENXZ+0x240c
xul.dll!?AsShadowLayer@Layer@layers@mozilla@@UAEPAVShadowLayer@23@XZ+0x37d8
xul.dll!?GetFontAt@gfxFontGroup@@UAEPAVgfxFont@@H@Z+0x536c
xul.dll!?GetType@ThebesLayer@layers@mozilla@@UBE?AW4LayerType@Layer@23@XZ+0x20f3
xul.dll!?UpdateFontList@gfxFontGroup@@UAEXXZ+0x7719
xul.dll!?UpdateFontList@gfxFontGroup@@UAEXXZ+0xab6
xul.dll!?UpdateFontList@gfxFontGroup@@UAEXXZ+0xa06
xul.dll!?UpdateFontList@gfxFontGroup@@UAEXXZ+0xef60
xul.dll!NS_CycleCollectorSuspect2_P+0x1d1
xul.dll!?CanDraw2D@gfx3DMatrix@@QBE_NPAUgfxMatrix@@@Z+0xa880