I noticed that Ladybird crashes when I have Hæck installed. It's a variant of the Hack font with ligatures.

Here's a gdb backtrace:

ak_verification_failed () at /home/paddi/clones/serenity/AK/Assertions.cpp:108
108	    __builtin_trap();
(gdb) bt
#0  ak_verification_failed () at /home/paddi/clones/serenity/AK/Assertions.cpp:108
#1  0x00007f6f9aeeb28c in AK::ErrorOr<AK::String, AK::Error>::release_value_but_fixme_should_propagate_errors ()
    at /home/paddi/clones/serenity/Meta/Lagom/../../AK/Error.h:202
#2  0x00007f6f9aee3d4d in OpenType::Name::string_for_id ()
    at /home/paddi/clones/serenity/Userland/Libraries/LibGfx/Font/OpenType/Tables.cpp:238
#3  0x00007f6f9aecc029 in OpenType::Name::family_name ()
    at /home/paddi/clones/serenity/Meta/Lagom/../../Userland/Libraries/LibGfx/Font/OpenType/Tables.h:341
#4  0x00007f6f9aec9425 in operator() ()
    at /home/paddi/clones/serenity/Userland/Libraries/LibGfx/Font/OpenType/Font.cpp:586
#5  0x00007f6f9aec9509 in OpenType::Font::family ()
    at /home/paddi/clones/serenity/Userland/Libraries/LibGfx/Font/OpenType/Font.cpp:58---Type <RET> for more, q to quit, c to continue without paging--

#6  0x00007f6f9aeb1f0f in operator() ()
    at /home/paddi/clones/serenity/Userland/Libraries/LibGfx/Font/FontDatabase.cpp:133
#7  0x00007f6f9aeb47c8 in operator() ()
    at /home/paddi/clones/serenity/Meta/Lagom/../../Userland/Libraries/LibCore/Resource.h:89
#8  0x00007f6f9aeb7989 in for_each_descendant<Core::Resource::for_each_descendant_file<Gfx::FontDatabase::load_all_fonts_from_uri(AK::StringView)::<lambda(const Core::Resource&)> >(Gfx::FontDatabase::load_all_fonts_from_uri(AK::StringView)::<lambda(const Core::Resource&)>&&) const::<lambda(const Core::Resource&)>&>(void) ()
    at /home/paddi/clones/serenity/Meta/Lagom/../../Userland/Libraries/LibCore/Resource.h:74
#9  0x00007f6f9aeb4ba8 in for_each_descendant<Core::Resource::for_each_descendant_file<Gfx::FontDatabase::load_all_fonts_from_uri(AK::StringView)::<lambda(const Core::Resource&)> >(Gfx::FontDatabase::load_all_fonts_from_uri(AK::StringView)::<lambda(const Core::Resource&)>&&) const::<lambda(const Core::Resource&)> >(void) ()
    at /home/paddi/clones/serenity/Meta/Lagom/../../Userland/Libraries/LibCore/Resource.h:76
#10 0x00007f6f9aeb4811 in for_each_descendant_file<Gfx::FontDatabase::load_all_fonts_from_uri(AK::StringView)::<lambda(const Core::Resource&)> >(void) ()
    at /home/paddi/clones/serenity/Meta/Lagom/../../Userland/Libraries/LibCore/Resource.h:86
#11 0x00007f6f9aeb26a0 in Gfx::FontDatabase::load_all_fonts_from_uri ()
    at /home/paddi/clones/serenity/Userland/Libraries/LibGfx/Font/FontDatabase.cpp:120
#12 0x0000564c399410af in Ladybird::FontPlugin::FontPlugin ()
    at /home/paddi/clones/serenity/Ladybird/FontPlugin.cpp:24
#13 0x0000564c3996d4d1 in serenity_main ()
    at /home/paddi/clones/serenity/Ladybird/WebContent/main.cpp:121

I used the font from here: https://github.com/ignatov/Haack/releases/download/0.1/Haeck-Regular.ttf