That's a great extension. Very handy

Works perfectly. Saves a lot of time for me. Many thanks to the author! The only problem is that I will need another extension for the German language, but there exist alternatives to this one.

Nice extension but there's one HUGE problem: it opens Wiktionary in the same tab, and there's no going back - the 'back' button simply turns gray

Problem: It opens the tab BEFORE the current tab (left of the current tab). This behaviour is weird. FireFox opens new tabs after the current tab (right).

Suggestion: Reuse existing tab. Say that I opened "dog" with this extension. Now if I open "cat", it opens a new tab. If this continues, there will be lots of Wiktionary tabs. If there already is a Wiktionary tab that this extension has opened, why not reuse the same tab?

Be careful with wiktionary, it's not a reliable dictionary, so be warned. But the extension works perfectly. But I'd like to be able to swich language. I also prefer the popup window rather a focussed new tab page.

Drawing attention away to a new tab is excessive.

Perhaps...
holding down [alt] brings up a bubble that can be clicked to open up a popup window (or straight to the popup, provided the kb shortcut can be modified).

Why not to show result in a popup window? That would be faster and not pollute tabs and history.