Mozilla is preparing for the inevitable version 100 of its Firefox browser, testing to make sure a triple-digit user agent won’t break the browser.

Web browsers send websites a string of text including the version number, rendering engine and more. Until now, there’s never been a web browser that has reached version 100, but Firefox is closing in at version 91.

Mozilla is testing to make sure the unprecedented version won’t cause any issues. In a bug post, the organization is trying an experiment to see if a triple-digit user agent breaks any sites.

We would like to run an experiment to test whether a UA string with a three-digit Firefox version number will break many sites. This new temporary general.useragent.experiment.firefoxVersion pref can override the UA string’s Firefox version.

If many sites are broken, we might need to freeze the UA string’s Firefox version at some two-digit number like “Firefox/99.0”: