After Chrome, Firefox will also support off-screen image lazy loading

Mozilla engineers plan to add support for “lazy loading,” a mechanism to defer the loading of images if they are not visible on the user’s screen when a website is first loaded.

Work on adding this feature in Firefox started last month. Google has already been testing a lazy loading mechanism in Chrome for over a year, since January 2018.

How lazy loading works

Lazy loading has been a part of the web development scene for more than a decade. It was initially created as a concept for JavaScript libraries.

Developers figured out that by delaying the loading of non-visible images, they could significantly improve a website’s page load time, a crucial search engine optimization (SEO) criteria, and, hence, obtain a better position in Google search results.

The concept spread quickly, and by the early 2010s, there were hundreds of libraries and plugins that provided easy ways to implement a lazy loading mechanism on websites, regardless of underlying programming language or content management system (CMS).

Google wanted to support lazy loading at the browser level

The first step to moving lazy loading from the website level to the browser level was taken in January 2018, when Google published a design document outlining how Chrome would support the lazy-loading of images and iframes that are outside a page’s visible section.

Chrome flags were later implemented, which are currently available in the Chrome stable version, and which users can enable and have websites load faster.

With Google’s backing, the feature also became attractive to other browsers, whose developers realized the benefits it could bring to improving page load times, if enabled.

Over the past year, Safari engineers have, too, expressed interest in supporting lazy loading.

With Firefox putting its backing behind the feature as well, this means that all major browser rendering engines will soon support lazy loading — WebKit (Safari), Blink (all Chromium browsers), and Gecko (Firefox).

We excluded EdgeHTML, as Microsoft Edge will soon move to a Chromium codebase.

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