Include jQuery in the JavaScript Console

Run this in your browser's JavaScript console, then jQuery should be available...

var jq = document.createElement('script');
jq.src = "https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js";
document.getElementsByTagName('head')[0].appendChild(jq);
// ... give time for script to load, then type (or see below for non wait option)
jQuery.noConflict();

NOTE: if the site has scripts that conflict with jQuery (other libs, etc.) you could still run into problems.

Update:

Making the best better, creating a Bookmark makes it really convenient, let's do it, and a little feedback is great too:

1. Right click the Bookmarks Bar, and click Add Page
2. Name it as you like, e.g. Inject jQuery, and use the following line for URL:

javascript:(function(e,s){e.src=s;e.onload=function(){jQuery.noConflict();console.log('jQuery injected')};document.head.appendChild(e);})(document.createElement('script'),'//code.jquery.com/jquery-latest.min.js')

Below is the formatted code:

javascript: (function(e, s) {
    e.src = s;
    e.onload = function() {
        jQuery.noConflict();
        console.log('jQuery injected');
    };
    document.head.appendChild(e);
})(document.createElement('script'), '//code.jquery.com/jquery-latest.min.js')

Here the official jQuery CDN URL is used, feel free to use your own CDN/version.

Run this in your console

var script = document.createElement('script');script.src = "https://code.jquery.com/jquery-3.4.1.min.js";document.getElementsByTagName('head')[0].appendChild(script);

It creates a new script tag, fills it with jQuery and appends to the head.

Copy everything from:
https://code.jquery.com/jquery-3.4.1.min.js

And paste it into console. Works perfectly.