- Internet browsers will interpret and render web pages differently, potentially responding differently based on width of the device
- Older browsers are often less capable, and require bespoke code to provide a consistent or substituted behaviour, which potentially degrades the user experience
- Fonts will render differently in each browser and screen size, risking distorted or inappropriately wrapped text
- JavaScript errors in different browsers can occur as some older browsers may not respond appropriately to recent JavaScript language functions, causing errors when interacting with the page
- Performance in older browsers may be poor and cause pages to load slowly