Firefox developer Mozilla warns users that when its browser – and when Google’s Chrome browser – reaches version 100, major websites are unlikely to correctly identify browsers, which may not work properly.
Firefox is currently at version 97, while Chrome is currently showing version 98. Once these are updated with three-digit version numbers, Mozilla says users may experience inconsistent issues across an unpredictable range of Web sites.
Mozilla explains that website servers look at something called the user agent to determine which browser is being used. They then use this information to configure the sites to display correctly.
Why can a three-digit version number be problematic?
When browsers first hit version 10 just over 12 years ago, many problems were discovered with the User-Agent parsing libraries, as the major version number jumped from one digit together.
Without a single specification to follow, different browsers have different formats for the User-Agent string and site-specific User-Agent parsing. It’s possible that some parsing libraries have assumptions or hard-coded bugs that don’t take major three-digit version numbers into account. Many libraries have improved parsing logic when browsers have moved to double-digit version numbers, so hitting the three-digit milestone should cause fewer problems. Chrome Team Engineer Mike Taylor did a survey of common UA parsing libraries that found no issues. Running Chrome experiments in the field revealed some issues, which we are currently working on.
What are browsers doing about it?
Both Firefox and Chrome have conducted experiments in which current browser versions report major version 100 to detect possible website crashes. This led to a few reported issues, some of which have already been fixed. These tests will continue until the release of version 100.
There are also backup mitigation strategies in place, in case version 100 on stable channels causes more damage to websites than expected.
Firefox and Chrome developers would run experiments, logging any problems they encountered. Currently, the list of sites reporting bugs with version 100 includes T-Mobile, Yahoo, and Daimler.
“If the outage is widespread and individual site interventions become unmanageable,” the blog post continues, “Mozilla may temporarily freeze the major version of Firefox at 99 and then test other options.”
Developers working on Google Chrome also have a “backup plan to use a flag to freeze the major version at 99”.