A common thing I do is Google stuff like "insertBefore mdn" because I just want to pull up a certain article quickly and I don't like w3schools. Of course, I need to click the (usually first) result Google gives me, but I'm lazy so I can't be bothered to do that. Hence, this Chrome extension. Whenever your search term contains "mdn" it just finds it on MDN immediately.
So, you can search MDN by simply having "mdn" among your Google search terms. For example, "insertBefore mdn", "MDN indexedDB" or "assertions mdn regex". The requirement there is that a space separates the "mdn" from the rest of the query. It will not care about capitalization, so "MDN abortsignal" works just as well as "mdn abortsignal".
If the article is not what you were looking for, you can just search MDN itself or omit "mdn" from your next search term.
If you're trying to Google something that has "mdn" in it but you don't want to find it on MDN, then you can either misspell MDN or make sure there's a non-space character stuck to the "mdn" part (e.g. "what is your favorite mdn$ page").