Running Ubuntu 16.04 and my computer slows down drastically after using my browser for a while

Question

This occurrence happens more frequently now than it did in the past. I mainly find that my computer slows down drastically when I watch YouTube, or, videos on Facebook.

I would have to say that it mostly happens when I watch videos on both browsers chrome and Firefox. Once it slows down the only way I can seem to bring it back is by restarting the machine. Even after I close the browser and run bleach-bit to clear the cache and what-not, the computer remains slow.

I tried disconnecting the internet connection and that doesn't fix it.

I tried restarting (successfully), but, that doesn't fix the problem either.

The system monitor doesn't show anything unusual running and even logging out and then back in does not seem to fix the issue up. As soon as I reboot, the system runs as smooth as ever.

Once I go to YouTube and watch a couple videos, the computer eventually just starts running really slow and never recoups from it till I reboot.

Any suggestion would be helpful.

Here is the output for free

              total        used        free      shared  buff/cache   available
Mem:        3834188     1095332      846100      241780     1892756     2165908
Swap:       3984380        4096     3980284

lscpu:

Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                2
On-line CPU(s) list:   0,1
Thread(s) per core:    1
Core(s) per socket:    2
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 37
Model name:            Intel(R) Pentium(R) CPU        P6100  @ 2.00GHz
Stepping:              5
CPU MHz:               939.559
CPU max MHz:           1999.0000
CPU min MHz:           933.0000
BogoMIPS:              3990.36
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              3072K
NUMA node0 CPU(s):     0,1
Flags:                 fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni dtes64 monitor ds_cpl est tm2 ssse3 cx16 xtpr pdcm pcid popcnt lahf_lm pti ssbd ibrs ibpb stibp dtherm arat flush_l1d

Here are the services that are running on my computer.

service --status-all:

 [ + ]  acpid
 [ - ]  alsa-utils
 [ - ]  anacron
 [ + ]  apache-htcacheclean
 [ - ]  apache2
 [ + ]  apparmor
 [ + ]  apport
 [ + ]  avahi-daemon
 [ + ]  binfmt-support
 [ + ]  bluetooth
 [ - ]  bootmisc.sh
 [ - ]  brltty
 [ - ]  checkfs.sh
 [ - ]  checkroot-bootclean.sh
 [ - ]  checkroot.sh
 [ + ]  console-setup
 [ + ]  cron
 [ + ]  cups
 [ + ]  cups-browsed
 [ + ]  dbus
 [ - ]  dns-clean
 [ + ]  grub-common
 [ + ]  hddtemp
 [ - ]  hostname.sh
 [ - ]  hwclock.sh
 [ + ]  irqbalance
 [ - ]  kerneloops
 [ - ]  keyboard-setup.dpkg-bak
 [ - ]  killprocs
 [ + ]  kmod
 [ + ]  lightdm
 [ + ]  lm-sensors
 [ - ]  mountall-bootclean.sh
 [ - ]  mountall.sh
 [ - ]  mountdevsubfs.sh
 [ - ]  mountkernfs.sh
 [ - ]  mountnfs-bootclean.sh
 [ - ]  mountnfs.sh
 [ + ]  network-manager
 [ + ]  networking
 [ + ]  nmbd
 [ + ]  ondemand
 [ + ]  openvpn
 [ - ]  plymouth
 [ - ]  plymouth-log
 [ - ]  pppd-dns
 [ + ]  procps
 [ + ]  rc.local
 [ + ]  resolvconf
 [ - ]  rsync
 [ + ]  rsyslog
 [ + ]  samba
 [ + ]  samba-ad-dc
 [ - ]  saned
 [ - ]  sendsigs
 [ + ]  smbd
 [ + ]  speech-dispatcher
 [ - ]  thermald
 [ + ]  udev
 [ - ]  ufw
 [ - ]  umountfs
 [ - ]  umountnfs.sh
 [ - ]  umountroot
 [ + ]  unattended-upgrades
 [ + ]  urandom
 [ - ]  uuidd
 [ - ]  virtualbox
 [ + ]  whoopsie
 [ - ]  x11-common

I installed a temperature sensor, here is the output.

dell_smm-virtual-0
 Adapter: Virtual device
 Processor Fan: 4749 RPM
 CPU:            +66.0°C  
 Other:          +66.0°C  
 Other:          +67.0°C  
 Other:          +81.0°C  

acpitz-virtual-0
 Adapter: Virtual device
 temp1:        +26.8°C  (crit = +100.0°C)
 temp2:         +0.0°C  (crit = +100.0°C)

coretemp-isa-0000
 Adapter: ISA adapter
 Core 0:       +77.0°C  (high = +80.0°C, crit = +90.0°C)
 Core 2:       +77.0°C  (high = +80.0°C, crit = +90.0°C)