I uninstalled it, because it's OK for English speakers, who want to translate everything in English, but if your destination language is not English, it's not useful, if you want to translate page already in English in another language, it says it can't because the page is already in English.
It's possible to change the destination language in the translation window, but I prefer to install an addon with more settings...
Concerning the bubble translation function, I'm not happy with that as it is, as I have some other addons with bubble function, and when I click on the bubble of this addon to have the translation, the popup fails to show (it is displayed 1 second, and then fade away), due to interaction with other bubbles. The context menu menu (in the settings) is much better than the bubble mode.
This addon is also called Panel view for Google translate, in the extension manager, I don't know why.