Some time ago, I wrote a bookmarklet to automatically open a new tab for the English-language Wiktionary entry for a word, either when that word is selected or when I am on one of my more common language-specific dictionary sites. I have now used this bookmarklet some thousands of times, so I can say that it works pretty well (unless the website I'm on is doing some hinky thing with its text).

Wiktionary is a communally edited dictionary of all words in all languages, although the coverage of some languages is much better than others. The "English-language Wiktionary," thus, is the dictionary of all words in all languages defined in English.

To use the bookmarklet as-is, just drag this link to the bookmarks bar of your browser: find on Wiktionary

Here is the raw code:

I have used this extensively in Firefox, and have also tested it in Chrome.