Hello,
I have Solus 4.3 Budgie DE and MANJARO Budgie DE 21.1.2 installed on bare metal on same type ( P/N ) of Desktop.
I have no speed difference beetween the 2 distro the only difference is that Solus uses less RAM than MNJRO.
( But I use Vivaldi and not Firefox anymore )
To test Net speed :
Either asked for a wget < URI of something >
Or try an youtube-dl -f "best[height<=720]" <youtube video URL>
The technical way is to use the equivalent of top/htop but for NetWork :
sudo su -c 'eopkg -y install iftop '; # Best Distro 🙂
sudo su -c 'pacman -Syyu iftop --noconfirm '; # MNJRO
Check the NetWork Interface your want to test ( ifconfig )
sudo iftop -i eno1
And
Ping Google with antother terminal ( ping 8.8.8.8 )
Then Do the same with an Video Streaming...
Best regards
Solus_Invictus
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Other Solution : Try Vivaldi because sadly Firefox has major issues and some MNJRO live USB as MANJARO Cinnamon DE 21.1.2. already use Vivaldi by deafault instead of Firefox
And, of course, ( sorry to say that but I've encoured cases like that ) never try performance on a Live USB they are very poor and usually not updated : The Worse is openSUSE Tumbleweed Live USB : Not recognized hardwares on LVU are fully functionnal on Final Isntallation ( That why openSUSE thakes 1h to 2h30 for a basic installaiton )