The Mozilla team pinpoints a potential issue that can cause breakage on sites. The team stated that version 100 of Chrome and Firefox, which will be released in the following months, may cause breakage on sites that rely on identifying the browser version to perform business logic. It is caused by a string sent in HTTP headers, named User-Agent string.
Some parsing libraries may have coded for assumptions or bugs that can cause problems with three-digit version numbers. Most of the libraries improved their parsing logic when a similar issue took place 12 years ago when browsers reached version 10. Mike Taylor from the Chrome team also did a survey of common UA parsing libraries that can cause problems.
The Mozilla team is inviting everybody to solve the issue. Both browsers are introducing a feature allowing users to configure the browser to report the version as 100, allowing them to test the possible issues. Website owners can also test their websites by checking the patterns that are problematic.
To configure Firefox Nightly to report the version as 100:
- Open Firefox Nightly’s Settings menu.
- Search for “Firefox 100” and then check the “Firefox 100 User-Agent String” option.
To configure Chrome to report the version as 100:
- Go to chrome://flags/#force-major-version-to-100
- Set the option to `Enabled`.