It likely comes as no surprise that third party content can be a significant contributor to slow loading websites and poor user experience. As performance engineers, we often need to find ways to balance requirements for their features with the strain that they can put on user experience. Unfortunately, for many sites this becomes a reaction to slowdowns and failures detected in production.

On Monday July 29th, DigiCert announced the need to revoke a large number of certificates due to a bug in domain validation. The CA/B Forum’s strict requirements to revoke these certificates within 24 hours resulted in a pretty busy Monday and Tuesday for a lot of folks. For some others, the deadline was moved to August 3rd due to exceptional circumstances. What remained a mystery was how many sites and third parties would be affected, how many would be prepared in time and what the impact of a mass revocation might look like across the web. In this blog post we’ll use the HTTP Archive to explore the impact.

HTTP compression is a mechanism that allows a web server to deliver text based content using less bytes, and it’s been supported on the web for a very long time. In fact the first web browser to support gzip compression was NCSA Mosaic v2.1 way back in 1993! The web has obviously come a long way since then, but today pretty much every web server and browser still supports gzip compression.

10 years ago, custom web fonts were a niche feature used by ~10% of websites. Today they are used by over 83% of websites! Fonts are generally loaded as a high priority resource, and some sites use techniques such as preload and early hints to get them to load as quickly as possible. Custom web fonts are important to many sites, since rendering with a specific typography is often preferred from a design perspective. However, this can easily become a performance issue when a large amount of fonts are loaded.

In May 2021 Microsoft announced that it would be officially retiring Internet Explorer in favor of the Chromium based Microsoft Edge. Usage for the legacy browser had been very low over the past few years, although many websites have still maintained polyfills for the older browser. In fact a number of my clients have recently told me that supporting IE 11 is required by their business, and is still a consideration when adding new features to their sites. I’m sure that the official retirement of Internet Explorer will help numerous organizations embrace modern web features and move on from some expensive polyfills. The official retirement date is June 15, 2022.

Largest Contentful Paint (LCP) is an important metric that measures when the largest element in the browser’s viewport becomes visible. This could be an image, a background image, a poster image for a video, or even a block of text. The metric is measured with the Largest Contentful Paint API, which is supported in Chromium browsers. Optimizing for this metric is critical to end user experience, since it affects their ability to visualize your content.

For the past 10 years, the HTTP Archive has tracked the evolution of the web by archiving the technical details of desktop and mobile homepages. During its early years, the Alexa top million dataset (which was publicly available until 2017) was used to source the list of URLs included in the archive and the number of sites tracked increased from 16K to almost 500K as testing capacity increased. To keep the archive current and include new sites, towards the end of 2018 we started using the Chrome User Experience Report as a source of the URLs to track.

Overview

Cookies are used on a lot of websites - 83.9% of the 5.7 million home pages tracked in the HTTP Archive to be specific. They are essentially a name/value pair set by a server and stored in a client’s browser. Sites can store these cookies by using the Set-Cookie HTTP response header, or via JavaScript (document.cookie). On subsequent requests, these cookies are sent to the server in a Cookie HTTP request header.