WP Simple Thimble

This plugin embeds or in-lines image/css/js content into the page before it’s loaded. This really improves page load speed scores, and can really improve actual load time if either the network connection is not blazingly fast, server side caching is used, or a combination of the two.

Warnings that are commonly eliminated in page load speed testing tools include

Optimize images
Leverage browser caching
Remove query strings from static resources
Specify image dimensions
Minify JavaScript
Minify HTML
Avoid bad requests
Avoid a character set in the meta tag
Avoid landing page redirects
Defer parsing of JavaScript
Inline small CSS
Inline small JavaScript
Minify CSS
Minimize request size
Optimize the order of styles and scripts
Put CSS in the document head
Serve resources from a consistent URL
Serve scaled images
Avoid CSS @import
Combine images using CSS sprites
Use a Content Delivery Network (CDN)
Reduce the number of DOM elements
Make fewer HTTP requests
Minify JavaScript and CSS
Put CSS at the top
Put JavaScript at bottom
Avoid AlphaImageLoader filter
Avoid CSS expressions
Reduce DNS lookups

The cases where some of these may still pop up would be a limitation of this project https://github.com/aadel112/simple-thimble, and you’ll note that these are all limitations that are actively being developed to be fixed.