Thanks for the feedback! We have a large number of improvements in the pipeline, we are going to release them soon (likely during the second half of this year).If you have specific examples of errors, that will help us.
There are currently two ways to achieve this.
1) From the Firefox main menu, there is a menu item to trigger translation.
2) Select text, right click, select the menu item to translate the selection, then from the translation dialog that shows up you...
