Sorry for my bad English and bad use of this forum...
I've installed Ubuntu-Mate on RPi 3B+, [ubuntu-mate-18.04.2-beta1-desktop-armhf+raspi-ext4.img], updated and upgraded without problem, installed Zram too.
All the system was directly installed on my SSD.
To read my mail in Thunderbird, no problem, but in Firefox, from 3-4 tabs, the mechanics begin to struggle and from 5 tabs, it's over, I have to stop everything hardly...
Ubuntu-Mate is in 32 bits.
The Linux kernel is the 4.15.0-1043-raspi2 armv7l
Proc: ARMv7 rev4.
Curiously, the memory used when I have 3 or four tabs open in Firefox is 750-800Mio, but the swap is almost zero!
I do not see Zram's action in the system.
If someone has any tricks to give me, I may have made a configuration error in the swappiness.
Another important question: What is the point of creating an image of Ubuntu Mate if you can not use it "normally"?
Thanks a lot form your answers, and sorry for my froggy english !
Philippe from France