As a rule of thumb, the design and functions on the pages/applications on if.xx sites should work well and look good in web browsers used in more than one percent of all sessions on all our sites.
Based on that and browser/browser version statistics for the if.xx sites, we proactively test functions and design in the latest versions of:
We test and make sure our solutions work well in these browser versions in mobile, tablet and desktop mode.
We do not proactively make sure that our sites work well or look good in other browsers or browser versions, but if we notice or get reports about e.g. an important function not working in a specific browser or version, we can decide to fix that issue.
We use browserl.ist to get out supported browsers. For a fully updated lists, you can check it out here