I built a static website for a client using SvelteKit, Tailwind, and Skeleton UI, hosted on Hetzner. Most of the site works normally, but one page is displayed incorrectly in Firefox on my client's Android phone and their partner's Android phone. The text is aligned to the left instead of centered, and some images appear stretched horizontally.
The problem occurs both on their home Wi-Fi and on 4G, which use the same ISP. It does not happen in other browsers. I have tested several Android devices, Firefox-based browsers, desktop browser device emulation, and an iPhone, but I cannot reproduce it.
Everything is served over HTTPS. The CSS is hosted locally, and the images are downloaded from the CMS during the build so the deployed site is fully static. Could the ISP be treating Firefox traffic differently, or is this more likely to be a device, browser version, extension, breakpoint, or CSS issue?
4 Answers
Connection speed could expose a race condition if styles are injected dynamically, but normal static CSS linked from the document should not load in the wrong order. Inspect the generated HTML and CSS on the affected device, and check whether a responsive rule, missing closing element, invalid nesting, or image-sizing rule is causing the layout to fall back.
Check the page on the actual Firefox Android app rather than relying only on desktop device emulation. Also temporarily disable Firefox’s privacy protections, content blockers, extensions, and any device-level ad blocker. If a stylesheet, font, script, or image is being blocked, the page can appear partially unstyled even though the site is static.
An ISP causing a Firefox-specific layout problem is extremely unlikely, especially with HTTPS. TLS prevents the ISP from modifying the HTML, CSS, or response headers without breaking the connection. At most, DNS or connectivity problems could prevent a resource from loading, but that would not normally selectively alter the layout on one page.
Since the CSS and images are served locally over HTTPS, a missing external stylesheet or CDN failure seems unlikely here.
I would first verify the exact Firefox version, Android version, screen size, display scaling, and accessibility settings on the affected phones. A device-specific breakpoint or a CSS rule that behaves differently at a particular viewport width could explain both the alignment and image sizing. Ask for a screenshot and compare the computed styles in remote debugging if possible.
Firefox’s built-in protection is worth testing, but because the assets are local, I would still inspect the browser’s network and console logs for failed requests before blaming the connection.