WiFi suddenly becomes deadly slow on browsers on Ubuntu 22.03

Today my WiFi connection got very slow apparently with no reason (at least, I can’t find one).

When I’m only using browser (Firefox standard) stay very low, around 50KiB/s with a few short-raises.

When I open Transmission and a fully-legal movie download from TPB download rates reaches 5 MB/s.

Illustrating:

Network traffic with Tranmission running:

Network traffic after Transmission being closed:

Network traffic with only youtube/firefox open:

What I’ve tried so far:

1. Change the MTU from wireless interface from 1500 to 1492;

2. Add to /etc/modprobe.d/iwlwifi.conf the following:

   options iwlwifi bt_coex_active=0 swcrypto=1 11n_disable=8
   

3. sudo systemctl restart NetworkManager.service

4. Set /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf variable wifi. from 3 to 2;

5. Upgrade Firefox version.

Does anyone have an idea?

Edit: Also tried this solution, but with no change:

• Limited HTTP traffic