SaneChoice Insights

Unravelling the Mystery: Why do Fonts Appear Differently in Firefox?

Modern office with laptops displaying browser software.

Fonts play a crucial role in shaping any digital landscape’s visual identity and user experience. However, a perplexing phenomenon has long plagued web developers and designers—the discrepancy in font rendering between different web browsers. Nowhere is this more evident than in Firefox, where the default handling of font weights can leave users scratching their heads.

In this blog article, we’ll delve into the intricacies of font behaviour, unravelling the reasons behind Firefox’s unique approach and how it impacts web content’s overall aesthetic and legibility. Prepare to embark on a journey that will enlighten you and empower you to take control of your typographic destiny, regardless of the browser.

The Conundrum of Font Weights

One of the primary sources of frustration for web developers and designers when working with Firefox is the browser’s default handling of font weights, particularly the use of the bolder keyword. This seemingly innocuous property can profoundly impact the appearance of text, especially when paired with the dynamic capabilities of variable fonts.

The Clash of Browsers

Regarding the default rendering of the <strong> and <b> elements, Chrome and Firefox take different approaches. Chrome and Safari opt for a consistent font-weight of 700 (bold), while Firefox follows the HTML standard’s recommendation of using the bolder keyword.

This divergence in implementation can lead to unexpected results, as the bolder value is a relative weight that adjusts based on the surrounding text’s font-weight. Variable fonts, where a wide range of weights are available, can result in significant visual discrepancies between the two browsers.

The Perils of “Bolder”

The bolder keyword, while well-intentioned, can sometimes fall short in its execution. When dealing with thin or lightweight fonts, the default increase in weight applied by Firefox may not be sufficient to make the <strong> or <b> elements stand out. This can lead to a scenario where the emphasised text becomes virtually indistinguishable from the surrounding content, undermining the intended visual hierarchy.

Navigating the Variable Font Landscape

The introduction of variable fonts has revolutionised web typography, offering designers and developers unprecedented control over font styles. However, this newfound flexibility also presents challenges when it comes to consistent rendering across different browsers.

The Chrome Conundrum

While Chrome’s default font-weight of 700 for <strong> and <b> elements may seem straightforward, it can falter when dealing with variable fonts. When the surrounding text has a font-weight above 550, the difference in weight becomes too small or even in the wrong direction, diminishing the visual impact of the emphasised text.

Firefox’s Inconsistent Approach

On the other hand, Firefox’s implementation of the bolder keyword, while more aligned with the HTML standard, suffers from its limitations. At lower font-weight values (around 300), the increase in weight applied to the <strong> and <b> elements may be too subtle, making the emphasised text difficult to distinguish.

Seeking a Harmonious Solution

As web designers and developers, we strive for consistency and predictability in typographic choices. The discrepancies between browser defaults, particularly in the context of variable fonts, present a significant challenge that demands a cohesive solution.

The Pursuit of Optimal Emphasis

Ideally, the <strong> and <b> elements should be easily identifiable, regardless of the font-weight of the surrounding text. Browsers could achieve this by applying a more standardised and visually impactful increase in weight, ensuring that the emphasised text stands out without compromising legibility.

Percentage-based Font Weights: A Promising Proposal

One potential solution discussed in the CSS Working Group is the introduction of percentage-based font-weight values. This approach would allow developers to specify a relative increase in weight, similar to how font-size can be adjusted using percentages. For example, a font-weight of 150% could provide a consistent and visually striking emphasis, regardless of the base weight of the surrounding text.

Is there a fix for web designers?

There is indeed a fix for website designers. Until there is some harmony of font rendering, you can add this to your CSS file (after testing), and your website should look like it does in other browsers.

html {
  -moz-osx-font-smoothing: grayscale;
  -webkit-font-smoothing: antialiased;
  -font-smoothing: antialiased;

Embracing the Future of Web Typography

As we navigate the ever-evolving landscape of web typography, it’s crucial to remain adaptable and proactive. Variable fonts and browser inconsistencies present challenges that present opportunities for innovation and collaboration within the web development community.

Staying Ahead of the Curve

By staying informed about the latest developments in font technologies and browser implementations, web designers and developers can anticipate and address potential issues before they arise. Engaging with industry discussions, following thought leaders, and actively participating in evolving web standards can help shape a more harmonious and user-friendly typographic experience.

Empowering Designers and Developers

Ultimately, the goal is to empower designers and developers with the tools and knowledge they need to create captivating, accessible, and consistent web experiences. By understanding the nuances of font behaviour and advocating for improved browser support, we can unlock the full potential of variable fonts and ensure that the written word on the web is a seamless and delightful experience for all users.


The discrepancies in font rendering between browsers, particularly Firefox’s unique approach to font weights, have long been frustrating for web designers and developers. However, this challenge also presents an opportunity for growth, innovation, and collaboration within the web community.

By exploring the intricacies of font behaviour, understanding the limitations of current browser implementations, and exploring promising solutions like percentage-based font weights, we can pave the way for a more harmonious and visually engaging typographic future on the web.

As we embrace the transformative power of variable fonts and continue to push the boundaries of web design, let us remain steadfast in our pursuit of consistency, legibility, and a delightful user experience – no matter the browser. Together, we can shape the evolution of web typography, empowering designers and developers to create captivating digital experiences that truly resonate with their audiences.

More from SaneChoice

Expand your mind by reading other articles and insights from SaneChoice

Elevate your understanding of technology with topics covering SEO, Web Hosting, Web Performance, Security and more.