Good functionality but it constantly uses 1% resources in Firefox task manager. I disabled pop-up buddle, translation history, translation providers, dictionaries and for a 1 hour after browser launch it used 4 997 313 processor resources (94 340 ms) but i didn't even use it. Consumption of installed uBlock, Gmail checker plus, Tampermonkey respectively: 9800 (3.2s), 2900 (1s), 3200 (0.6s).
Updated to 15.12 and it actually not fixed for me. The same behavior

окошко маленькое и не растягивается

A great addition. I often use it. This is what I needed :-)

It shows a loading screen and never translates!