Fifth sometimes crashes in the web-mail interface of seznam.cz. This interface seems to be ajax-based. I cannot state a specific condition when it crashes, but it seems that it happens preferably when performing some action after a while of inactivity.
This will be hardly reproducible for you: You would have to create an account there, have some e-mails there and work with them, while the interface is in Czech. However, here is some gdb output:
Program received signal SIGPIPE, Broken pipe.
0x00007ffff608735d in write () from /lib/x86_64-linux-gnu/libpthread.so.0
(gdb) bt
#0 0x00007ffff608735d in write () from /lib/x86_64-linux-gnu/libpthread.so.0
#1 0x00007ffff3b9f7f6 in ?? () from /lib/x86_64-linux-gnu/libcrypto.so.1.0.0
#2 0x00007ffff3b9d89b in BIO_write () from /lib/x86_64-linux-gnu/libcrypto.so.1.0.0
#3 0x00007ffff3ebcdb2 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#4 0x00007ffff3ebe993 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#5 0x00007ffff3ebae52 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#6 0x00007ffff414864e in ?? () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#7 0x00007ffff411952b in ?? () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#8 0x00007ffff411c648 in ?? () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#9 0x00007ffff412c630 in ?? () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#10 0x00007ffff412d181 in curl_multi_perform () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#11 0x000000000170178c in WebCore::ResourceHandleManager::downloadTimerCallback(WebCore::Timer<WebCore::ResourceHandleManager>*) ()
#12 0x00000000017066b6 in void std::_Mem_fn<void (WebCore::ResourceHandleManager::*)(WebCore::Timer<WebCore::ResourceHandleManager>*)>::operator()<WebCore::Timer<WebCore::ResourceHandleManager>*&, void>(WebCore::ResourceHandleManager*, WebCore::Timer<WebCore::ResourceHandleManager>*&) const ()
#13 0x00000000017064a7 in void std::_Bind<std::_Mem_fn<void (WebCore::ResourceHandleManager::*)(WebCore::Timer<WebCore::ResourceHandleManager>*)> (WebCore::ResourceHandleManager*, WebCore::Timer<WebCore::ResourceHandleManager>*)>::__call<void, , 0ul, 1ul>(std::tuple<>&&, std::_Index_tuple<0ul, 1ul>) ()
#14 0x00000000017060b8 in void std::_Bind<std::_Mem_fn<void (WebCore::ResourceHandleManager::*)(WebCore::Timer<WebCore::ResourceHandleManager>*)> (WebCore::ResourceHandleManager*, WebCore::Timer<WebCore::ResourceHandleManager>*)>::operator()<, void>() ()
#15 0x0000000001705ca9 in std::_Function_handler<void (), std::_Bind<std::_Mem_fn<void (WebCore::ResourceHandleManager::*)(WebCore::Timer<WebCore::ResourceHandleManager>*)> (WebCore::ResourceHandleManager*, WebCore::Timer<WebCore::ResourceHandleManager>*)> >::_M_invoke(std::_Any_data const&) ()
#16 0x000000000046c2e4 in std::function<void ()>::operator()() const ()
#17 0x00000000017069f6 in WebCore::Timer<WebCore::ResourceHandleManager>::fired() ()
#18 0x00000000004af861 in WebCore::ThreadTimers::sharedTimerFiredInternal() ()
#19 0x00000000004af751 in WebCore::ThreadTimers::sharedTimerFired() ()
#20 0x0000000000ab6ddd in WebCore::callback(void*) ()
#21 0x0000000001ad8b53 in Fl::wait(double) ()
#22 0x00000000004158df in main (argc=<optimized out>, argv=<optimized out>) at main.cpp:821
Is that helpful? I have not yet terminated gdb, so I can execute more gdb commands if you wish and if you reply quickly.