I Found 5 Performance Issues on This Horizon Theme Store - Here is How I Fixed All of Them
Yes - the Horizon theme is a solid theme choice. It looks clean, it's elegant and easily customizable. The successor of the Dawn theme is doing wonders. However, even though it is undoubtedly a good starter choice, the addition of apps, images and bloat code can make even the best of the themes slow.
This is what was happening with this particular store that came to me scoring 62 on mobile and 68 on desktop; most definitely not terrible, but not ideal either.
After the optimization, both scores hit 98.
Here is exactly what was wrong and how I fixed it.
What Google PageSpeed Insights Found
The audit revealed several issues that were stacking on top of each other; each one adding precious seconds to the load time.
Largest Contentful Paint (LCP) of 19~ seconds on mobile. LCP measures how long it takes for the main content of your page to appear. At this speed, visitors were staring at a blank or partially loaded screen for nearly 20 seconds before seeing anything meaningful. Most of them left long before that.
Poor image delivery. Images were uncompressed and not optimized for web delivery; accounting for 2MB of unnecessary data being downloaded on every page load. Modern formats like WebP and AVIF were not being used.
Inefficient cache lifetimes. The store was forcing returning visitors to re-download 3MB of assets they had already loaded on a previous visit. This is a lot! Every repeat visitor was being treated like a first-time visitor by the server.
Render-blocking requests adding 1s of delay. Critical CSS and JavaScript were loading in a way that prevented the page from displaying anything until they finished; adding over a full second of blank screen time before a single pixel appeared.
Unused CSS and JavaScript. 74 KiB of unused CSS and 113 KiB of unused JavaScript were being loaded on every page; code that served no purpose but still had to be downloaded and processed by the browser.
What I Did to Fix It
Every fix was done manually; no speed optimization apps, no automated tools that often add more bloat than they remove.
First things first: images. I manually optimized and compressed every image on the store. I started by converting them to WEBP, implementing proper lazy loading so images only load when they are about to enter the viewport, and resizing when appropriate. Image delivery savings went from 2mb~ down to 58kb!
After that, I addressed the cache lifetime configuration so that returning visitors load the store from cached assets instead of downloading everything fresh.
Finally I resolved the render-blocking issue by deferring and async-loading non-critical JavaScript and inlining critical CSS; reducing render-blocking time from 1,010ms down to 30ms.
I removed unused CSS and JavaScript; cleaning up stylesheet bloat from 74 KiB down to 13 KiB and eliminating the unused JavaScript entirely from the critical path.
The Results
Mobile score: 62 to 98
Desktop score: 68 to 98
LCP: 19.2s to 1.8s on mobile
Total Blocking Time: 250ms to 0ms
CLS: 0.014 to 0.001
Here is the proof, live on PageSpeed Insight
Ok, But Honestly, Does Any of This Actually Affect Sales?
A score of 98 looks great on paper; but what does it mean for your business?
According to Shopify's own research, every 1-second delay in mobile load time drops conversions by up to 20%. This store had an LCP of 19.2 seconds on mobile; meaning visitors waited nearly 20 seconds for the main content to appear. Google's data shows that 53% of mobile visits are abandoned if a page takes longer than 3 seconds to load.
Every visitor who landed on this store during a slow period was overwhelmingly likely to leave before buying anything. And because Google uses Core Web Vitals as a ranking signal; a slow store also ranks lower in search results; meaning fewer visitors in the first place.
Speed is not a technical detail. It is a direct revenue lever.
Is Your Shopify Store Slow?
If you are running Horizon (or any other Shopify theme, really) and you are not sure how your store performs, I'm here for you! Let me audit your store and tell you where it stands. 100% free, no obligation to proceed.