Security News > 2021 > August > 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.
The current user agent for Mozilla Firefox version 90 is listed below.
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.
When conducting the test, a 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.
While Slack quickly fixed this issue, it illustrates how simple coding errors can produce unexpected results when the user agent changes to version 100.
If continued tests show that many sites are broken by the new user agent, Firefox is may freeze the user agent to a two-digit number like "Firefox/99.0.".