Mozilla Firefox and Google Chrome Browsers May Cause Issues Upon Reaching Version 100

Actions to Take

Bring this Support Notice to the attention of your Information Technology department or Webmaster. Consider testing your websites according to instructions from Mozilla.


Mozilla is soon to release a Firefox version 100 web browser and Google is soon to release a Chrome version 100 web browser. The switch from a two-digit version number to a three-digit version number may cause breaking changes on some websites.

Essent Service Impact Analysis

Essent products and services are not affected by the change.

In order to identify a browser type, servers use a variety of parsers to interpret User-Agent strings that are sent by browsers. Some parsers may be hardcoded for two-digit version numbers or otherwise have bugs that will result in breaking changes when the User-Agent string provides a version number that is three digits.

Essent software can handle version numbers with three or more digits when processing User-Agent strings and is not affected by this issue.

Corrective Action

No corrective action is required in relation to Essent products and services.

Custom code and integration points should be checked for compatibility with the new User-Agents before they are released and any issues corrected.

Firefox provides testing instructions at the end of this post: Follow the instructions for website maintainers to determine whether your custom code is affected.

More information

Chrome 100 is scheduled for release on March 29, 2022. Firefox 100 is scheduled for release on May 3, 2022.

"This has the potential to cause breakage on sites that rely on identifying the browser version to perform business logic,” according to a Mozilla post that explains the issue and mitigation steps.

The full Mozilla post is here.

Chrome provides more information here:

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