Periodic crash of extremely simple esp8266 sketch

I'm quite new to esp8266 and even to electronics topic, so don't be surprised with the question.

I've uploaded extremely simple script to esp8266-07 from Arduino IDE. It starts (sometimes...) works for multiple loops, then crashes and restarts. Below will be listed connection schema, sketch and serial output. What's wrong?

RESET is not connected. After sketch is uploaded I disconnect GPIO0 from GND, turn off and on VCC.

Also I don't know what is "firmware" and should I additionally upload it somehow.

Sketch:

void setup() {
    Serial.begin(115200);
    Serial.println("Setup");
}

void loop() {
    Serial.println("loop");
    delay(1000);
}

And output:

Setup
loop
loop
loop
loop
loop
loop
loop
loop

Exception (0):
epc1=0x402067fe epc2=0x00000000 epc3=0x00000000 excvaddr=0x0000004e depc=0x00000000

ctx: sys
sp: 3ffff1c0 end: 3fffffb0 offset: 01a0

>>stack>>
...
<<stack<<

ets Jan 8 2013,rst cause:2, boot mode:(3,0)

load 0x4010f000, len 1384, room 16
tail 8
chksum 0x2d
csum 0x2d
v09f0c112
~ld
)Setup
loop
loop
loop
loop
loop
loop
loop
loop

Exception (0):
epc1=0x402067fe epc2=0x00000000 epc3=0x00000000 excvaddr=0x0000004e depc=0x00000000

ctx: sys
sp: 3ffff1c0 end: 3fffffb0 offset: 01a0

>>stack>>
...
<<stack<<

ets Jan 8 2013,rst cause:2, boot mode:(3,0)

load 0x4010f000, len 1384, room 16
tail 8
chksum 0x2d
csum 0x2d
v09f0c112
~ld
)Setup
loop
loop
loop
loop
loop
loop
loop
loop
loop
loop

Actual stack content is replaced with "..."

Arduino IDE 1.6.5, board manager 2.1.0

Same test for Arduino IDE 1.6.8 and 2.3.0 crashes even without setup :(

Yeah, @dandavis was right - RESET was the reason. But actually it WAS floating, I pulled it up like it was suggested on the original diagram and it worked)