This is the most user friendly translation option I've found for Firefox Mobile. If you have a fork of Firefox Android (such as Mull), you can add this to a custom collection to use it on your phone. I usually leave it disabled and, when I need something translated, turn it on to show the translation bar at the bottom of the screen.

Sometimes, "show original" function doesn't work.

TO THE DEVELOPER:
If possible, when I select a sentence in a foreign language and right-click to use your addon, it would be great if you could add what is the name of the foreign language translated. Thanks.

I am so happy with this addon, it works really well.
Previously, I was using the translate addon that has the biggest number of users but it could not even translate Instagram pages that were in Russian. Using this addon, it is very easy to do that automatically for Instagram or any other sites.

Many thanks to the developer of this addon.

GOOD

Edit: It's fixed! Thank-you, Dev.

Newest update ruined this addon. It is unreadable because of transparency.

Basically good and outstandingly convenience translation tool, which makes web pages readable in any language. However, suddenly pop-up translation window became quite annoying transparent one. I prefer the one shown in your screenshots. Is this an effect of Firefox update? I also prefer translation by deepL WITHOUT another tab opened, than transparent window. Thank you.

Al seleccionar un texto se cuenta con un icono auxiliar al lado y permite una correcta traducción del texto. Es intuitivo, agradable, y fácil de usar y configurar.

Convenient and fast

Me encanat

Thank you brought this extension to this world, godbless you my brothers & sisters.

Wonderful

This should be the recommended translation extension, when translating a webpage it doesn't take you to a new tab like the others.