Kali playing system sound but no browser or other app sound

Hello everyone, I am really new here so I will say sorry in advance if I don't do anything correctly.

I have just installed Kali Linux on my laptop (Toshiba Satellite P50-A-14G) with Windows and Ubuntu.
I am using Ubuntu's installation GRUB because I wasn't able to install Kali in UEFI mode and create a functional dual boot with Windows 10.

Until yesterday, I haven't used Kali for playing any kind of sound. But I was trying to watch a video in YouTube and I realized that there weren't playing any sound at all!! :(
I have been searching in many sites trying to solve the problem but it was for nothing.

After adding "pulseaudio --system" command to a script in /etc/init.d/[myscript] I can play system sounds every time I boot Kali. For example, when I press the button to raise or down the volume, I can hear the "pop". Moreover, when I am in a terminal and I press tab key for suggestions and there aren't suggestions for that command I can hear the "blip". Moreover, I can play MP3 files or listen to some videos.
However, if I open Firefox and I access YouTube to play a video, I can't hear NOTHING.

Please, could anyone help me? I also have tried to install "alsa-mixer" but I cannot solve the problem.

Here is the output of lspci command:

Code:

---

root@kali:~# lspci
00:00.0 Host bridge: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor DRAM Controller (rev 06)
00:01.0 PCI bridge: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor PCI Express x16 Controller (rev 06)
00:02.0 VGA compatible controller: Intel Corporation 4th Gen Core Processor Integrated Graphics Controller (rev 06)
00:03.0 Audio device: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor HD Audio Controller (rev 06)
00:14.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB xHCI (rev 04)
00:16.0 Communication controller: Intel Corporation 8 Series/C220 Series Chipset Family MEI Controller #1 (rev 04)
00:1a.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB EHCI #2 (rev 04)
00:1b.0 Audio device: Intel Corporation 8 Series/C220 Series Chipset High Definition Audio Controller (rev 04)
00:1c.0 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #1 (rev d4)
00:1c.2 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #3 (rev d4)
00:1c.3 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #4 (rev d4)
00:1d.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB EHCI #1 (rev 04)
00:1f.0 ISA bridge: Intel Corporation HM86 Express LPC Controller (rev 04)
00:1f.2 SATA controller: Intel Corporation 8 Series/C220 Series Chipset Family 6-port SATA Controller 1 [AHCI mode] (rev 04)
00:1f.3 SMBus: Intel Corporation 8 Series/C220 Series Chipset Family SMBus Controller (rev 04)
01:00.0 3D controller: NVIDIA Corporation GK107M [GeForce GT 745M] (rev a1)
03:00.0 Network controller: Intel Corporation Wireless 3160 (rev 83)
04:00.0 Ethernet controller: Qualcomm Atheros QCA8171 Gigabit Ethernet (rev 10)

---

Please, help me :(

Thanks in advance to everyone!!