Mozilla Tests If 'Firefox/100.0' User Agent Breaks Websites

Mozilla has launched an experiment where they change the Firefox browser user agent to a three-digit "Firefox/100.0" version to see if it will break websites. Bleeping Computer reports: A user agent is a string used by a web browser that includes information about the software, including its name, version, and technologies that it uses. When a new version of a browser is released, the developers also increment the version number in the user agent string. When visiting a website, the user agent strings are sent to a website so that the site knows the software capabilities of the visitor. This information allows the website to modify its response to account for different features of browsers. As Firefox version numbers are currently two digits, Mozilla developers are investigating if anything breaks when they release Firefox Nightly version 100 in March 2022. "We would like to run an experiment to test whether a UA string with a three-digit Firefox version number will break many sites," Mozilla Staff Engineering Program Manager Chris Peterson said in a bug post first spotted by Techdows. "This new temporary general.useragent.experiment.firefoxVersion pref can override the UA string's Firefox version." When conducting the test, an enrolled Firefox user will have their user agent changed to the following string with the hopes that if anything breaks, they will report it to Mozilla: "Mozilla/5.0 (Windows NT 10.0; rv:100.0) Gecko/20100101 Firefox/100.0."

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