Not all browsers are made equal.
Chrome, Firefox, and Safari showing differences in font rendering.
A website is just a set of instructions describing how a site should look. It's up to the browser to render it, and every browser renders things a little differently. For example, a common problem we've run in to is that Chrome and Firefox round percentages differently which can cause responsive layouts to break at different resolutions.
When someone finds an inconsistency, we ask them to give us the details of their environment and provide a screenshot (if possible) of the issue. Providing technical details doesn't have to be intimidating, we use Support Details to quickly and accurately get a clear picture of their environment. Once we have that, we can attempt to recreate the issue and address it.