Sorry for the inconvenience. Because the translation result is from online service, I think it's not good to translate immediately after every double clicks. Different than offline-based translation addons, mine suffers from slower speed on crappy internet, not mention that every time double clicked a popup will cover some of page content, and the privacy issues (imagine everything you double clicked will be sent instantly to online provider, even if you want to translate your selected string or not). Still, I understand your will and I'll try to do something about it soon.

That's weird. Could you provide some sites URL as example, or it's completely random?
The button does not show most of the time if you select text on the web, and when the button does appear, clicking on it does not show anything, am I right?
Remember that "green button" does not support all sites, like this one (addons.mozilla.org).
And what are your firefox version number? If you have time to provide more detailed information, you can contact with me by my email tranthang.yb@outlook.com.