It works, but on every page I visit, it says that a script is blocking the direct opening, it shows "open PUD", and only when clicking it, it opens up the popup with the definition. So, no problem, it works, but there's probably something that bugs a little, as there's this warning message.

The brilliant point is that we can add custom dictionaries!

If you find a way to make it work without the need to watch a SILENT how-to video, I'll come back to try it. In the meantime, I'll find an alternative.

Works somewhat. I added google translate and had to set it to open in a new tab, otherwise it wouldn't work (a green prompt). As of now I can double tap a word and it will open in google translate, but the annoying prompt is still there.
I use Android.
To conclude, three stars.

doesn'ẗ work, only shows a prompt to open PUD and when you do the pop-up is empty

For mobile doesn't work or it's quite complex to make it work - En los móviles no funciona o es muy difícil hacerlo funcionar.

howto make it works in input text area?

Prevents you from selecting a text and using right click (to copy it or search for in the Google).
The dictionary itself works good.

Works great, but sometimes picking a different dictionary doesn't take effect until I reload the tab

Thank you very much, very good addon.
Para los que quieran poner la página de la RAE, esta es la dirección para incluir en las opciones del diccionario
http://dle.rae.es/$$

https://i.imgur.com/5ntcsgL.png

It's quite convenient!
you can add various dictionary.

Good concept. Doesn't work when i try to save a dictionary though

Loved the extension where it performs much better then google dictionary extension by adding more details in showing. Well done, get an android app and try to bring it on google extension which will help you go over other browsers such as opera, brave and Vivaldi.

It's very wonderful add-on for me. But, I can't use usual selecting and right-clicking with this add-on. I want to use "Context Search" (which make it possible to search selected text from context menu) and this add-on together. I wish to become it possible.

i find this extension really useful and simple

Thanks. The new version is better as you can use a pop-up window which overcomes the problem of mixed content. The popup window is scrollable, movable & resizable too.

Excellent little addon. Great replacement for an addon I previously had that no longer works in the new FF.

Couple of suggestions...
Replace the horrible 'Open PUD' anchor with the addon icon instead.
Add a user definable offset for where the anchor appears relative to the selected text, so it can be redefined by the user so as not to interfere with other addon anchors people may have.
Make the 'Hover to anchor' display the popup at the mouse position and when the mouse leaves the popup remove the popup.

I followed your instructions to add a dictionary and clicked the Save button; but nothing happened. Only the Cancel button works.
Can you please advise fix?

This works for English definitions but not by default.
Go to settings.
1. Only check Enable Pop-Up Dictionary or you might not get the window.
2. Replace default dictionary with:
http://www.wordreference.com/definition/$$
as the standard one translates to French.
3. Double-click or highlight a word to get your definition.
It becomes harder using other right-click functionality, but you can manage.

Should include proper instructions on how to use this with proper examples
Its default dictionary does not work at all

When I double click a word a box with English to French translation comes to screen and I do not know French, unfortunately. Can the dictionary be changed someway, that is do I have to first upload a new dictionary and how? I would like to see a unknown word defined in English, this is usually enough to grasp about the word's meaning.
The options page doesn't offer any solution.
Earlier a word's definition could be found with just a double click, perhaps together with alt or cntrl key, and a box with synonyms appeared on the screen. Or is this not permitted with the latest Firefox version? Babylon and Dictionary.com with this kind operation were very useful add-ons and are missed greatly now.
Otherwise Pop-up dictionary has many advantages over other similar add-ons. Thanks very much !
Matti Ollikainen