I can understand to you, but I don't have more accurated data.

Yes, always it happens: I do install lightspark, I do open IceCat ... and IceCat crashes. I do uninstall lightspark, I do open IceCat ... and IceCat works perfectly. I'm not using FireFox right now.

These are the messages from console:

[user@archerpc ~]$ icecat --debug
INFO: A plugin was found. Adding it to the list.
ERROR: findPluginInList: no plugin found in list
INFO: The plugin Pulse plugin output only was added with backend: pulseaudio
INFO: the selected backend is: pulseaudio
INFO: get_plugin: pulseaudio
INFO: RenderThread this=0x7f6b1c761000
INFO: Font File is /usr/share/fonts/TTF/DejaVuSerif.ttf
INFO: Creating input thread
INFO: X Window 9e23bd6 Width: 610 Height: 160
ERROR: Resize not supported
ERROR: Resize not supported
INFO: Newstream for http://fullsoftgamer.org/wp-content/themes/fullsoftgamer2/images/doodles/logoNavidad.swf
INFO: Compressed SWF file: Version 10 Length 89656
INFO: FrameRate 24
INFO: Creating VM
INFO: Global is 0x7f6b1b8163e0
INFO: SWF Metadata:
        #text:           
        CreatorTool:            Adobe Flash Professional CS5
        #text:           
        CreateDate:             2010-12-04T18:14:29-05:00
        #text:           
        MetadataDate:           2010-12-05T16:00:27-05:00
        #text:           
        ModifyDate:             2010-12-05T16:00:27-05:00
        #text:           
        #text:           
        InstanceID:             xmp.iid:2853A176152068118083FE049454B95F
        #text:           
        DocumentID:             xmp.did:2853A176152068118083FE049454B95F
        #text:           
        OriginalDocumentID:             xmp.did:F77F11740720681188C6DD4109A0A859
        #text:           
        DerivedFrom:             xmp.iid:F77F1174072068118083FE049454B95F xmp.did:F77F11740720681188C6DD4109A0A859 xmp.did:F77F11740720681188C6DD4109A0A859 
        #text:           
        #text:           
        format:         application/x-shockwave-flash
        #text:           
Chosen config 0x7f6b1b46a660
INFO: Fragment shader compilation 
INFO: Vertex shader compilation 
INFO: Vertex shader compilation 
131072
65536
0
INFO: FPS: 23
INFO: DestroyStream on main stream
INFO: End of parsing @ 89648
INFO: FPS: 24
INFO: A plugin was found. Adding it to the list.
ERROR: findPluginInList: no plugin found in list
INFO: The plugin Pulse plugin output only was added with backend: pulseaudio
INFO: the selected backend is: pulseaudio
INFO: get_plugin: pulseaudio
INFO: RenderThread this=0x7f6b0bd99000
INFO: Font File is /usr/share/fonts/TTF/DejaVuSerif.ttf
INFO: Creating input thread
INFO: X Window 9e25e2b Width: 480 Height: 270
ERROR: Resize not supported
ERROR: Resize not supported
INFO: A plugin was found. Adding it to the list.
ERROR: findPluginInList: no plugin found in list
INFO: The plugin Pulse plugin output only was added with backend: pulseaudio
INFO: the selected backend is: pulseaudio
INFO: get_plugin: pulseaudio
INFO: RenderThread this=0x7f6b0bdbb000
INFO: Font File is /usr/share/fonts/TTF/DejaVuSerif.ttf
INFO: Creating input thread
INFO: X Window 9e25e2d Width: 464 Height: 376
ERROR: Resize not supported
ERROR: Resize not supported
INFO: FPS: 24
INFO: FPS: 24
INFO: A plugin was found. Adding it to the list.
ERROR: findPluginInList: no plugin found in list
INFO: The plugin Pulse plugin output only was added with backend: pulseaudio
INFO: the selected backend is: pulseaudio
INFO: get_plugin: pulseaudio
INFO: RenderThread this=0x7f6b0bb3b800
INFO: Font File is /usr/share/fonts/TTF/DejaVuSerif.ttf
INFO: Creating input thread
INFO: X Window 9e27f7f Width: 620 Height: 376
ERROR: Resize not supported
ERROR: Resize not supported
INFO: Newstream for http://www.youtube.com/v/1X6yuW40iw0&ap=%2526fmt%3D18
INFO: Compressed SWF file: Version 8 Length 1987
INFO: DestroyStream on main stream
INFO: FrameRate 31
INFO: ExportAssetsTag Tag
ERROR: Not supported action opcode
INFO: End of parsing @ 1979
INFO: A plugin was found. Adding it to the list.
ERROR: findPluginInList: no plugin found in list
INFO: The plugin Pulse plugin output only was added with backend: pulseaudio
INFO: the selected backend is: pulseaudio
INFO: get_plugin: pulseaudio
INFO: RenderThread this=0x7f6b0bbb7c00
INFO: Font File is /usr/share/fonts/TTF/DejaVuSerif.ttf
INFO: Creating input thread
INFO: X Window 9e27f81 Width: 620 Height: 376
ERROR: Resize not supported
ERROR: Resize not supported
INFO: Newstream for http://www.youtube.com/v/37sKI7d7-xA&ap=%2526fmt%3D18
INFO: Compressed SWF file: Version 8 Length 1985
INFO: DestroyStream on main stream
INFO: FrameRate 31
INFO: ExportAssetsTag Tag
ERROR: Not supported action opcode
INFO: End of parsing @ 1977
Chosen config 0x7f6aeb31cac0
Chosen config 0x7f6aeb3173c0
INFO: Fragment shader compilation 
INFO: Fragment shader compilation 
INFO: Vertex shader compilation 
INFO: Vertex shader compilation 
INFO: Vertex shader compilation 
INFO: Vertex shader compilation 
INFO: A plugin was found. Adding it to the list.
ERROR: findPluginInList: no plugin found in list
INFO: The plugin Pulse plugin output only was added with backend: pulseaudio
INFO: the selected backend is: pulseaudio
INFO: get_plugin: pulseaudio
INFO: RenderThread this=0x7f6b0bbbe800
131072
65536
0
INFO: Font File is /usr/share/fonts/TTF/DejaVuSerif.ttf
INFO: Creating input thread
131072
65536
0
INFO: X Window 9e28130 Width: 620 Height: 376
ERROR: Resize not supported
ERROR: Resize not supported
INFO: Newstream for http://www.youtube.com/v/BQn6Qb-9mD8&ap=%2526fmt%3D18
INFO: Compressed SWF file: Version 8 Length 1971
INFO: DestroyStream on main stream
INFO: FrameRate 31
INFO: ExportAssetsTag Tag
ERROR: Not supported action opcode
INFO: End of parsing @ 1963
INFO: A plugin was found. Adding it to the list.
ERROR: findPluginInList: no plugin found in list
INFO: The plugin Pulse plugin output only was added with backend: pulseaudio
INFO: the selected backend is: pulseaudio
INFO: get_plugin: pulseaudio
INFO: RenderThread this=0x7f6ae1789800
INFO: Font File is /usr/share/fonts/TTF/DejaVuSerif.ttf
INFO: Creating input thread
INFO: X Window 9e28132 Width: 620 Height: 376
ERROR: Resize not supported
ERROR: Resize not supported
INFO: Newstream for http://www.youtube.com/v/E9I-Onwfqpo&ap=%2526fmt%3D18
INFO: Compressed SWF file: Version 8 Length 1962
INFO: DestroyStream on main stream
INFO: FrameRate 31
INFO: ExportAssetsTag Tag
ERROR: Not supported action opcode
INFO: End of parsing @ 1954
INFO: A plugin was found. Adding it to the list.
ERROR: findPluginInList: no plugin found in list
INFO: The plugin Pulse plugin output only was added with backend: pulseaudio
INFO: the selected backend is: pulseaudio
INFO: get_plugin: pulseaudio
INFO: RenderThread this=0x7f6ae178f800
INFO: Font File is /usr/share/fonts/TTF/DejaVuSerif.ttf
INFO: Creating input thread
INFO: X Window 9e28134 Width: 620 Height: 376
ERROR: Resize not supported
ERROR: Resize not supported
INFO: Newstream for http://www.youtube.com/v/yp6cB7BGj48&ap=%2526fmt%3D18
INFO: Compressed SWF file: Version 8 Length 1983
INFO: DestroyStream on main stream
INFO: FrameRate 31
INFO: ExportAssetsTag Tag
ERROR: Not supported action opcode
INFO: End of parsing @ 1975
Chosen config 0x7f6b0e555f60
Chosen config 0x7f6ad0921860
Chosen config 0x7f6ad008f160
INFO: Fragment shader compilation 
INFO: Fragment shader compilation 
INFO: Fragment shader compilation 
INFO: Vertex shader compilation 
Segmentation fault
[user@archerpc ~]$