In brief: Reaching version 100 should be a milestone for a web browser, but it's actually an event that could break some websites for people who use Google Chrome, Microsoft Edge, or Mozilla's Firefox. Developers have been preparing for this moment for a while now, but they still need help.
Chrome, Microsoft Edge, and Firefox are all inching closer to the release of their 100th version. While this may look like a nice round number to a user, it also has the potential to introduce bugs or create compatibility issues for certain websites.
For some people it may even bring back memories of the infamous Y2K bug and Microsoft skipping Windows 9, but this time around the issue is related to how websites read user-agent (UA) strings to identify your web browser and its capabilities.
When you visit a webpage on a site like TechSpot, your device sends a request for that page that includes a user agent string that looks something like this: "Firefox: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:96.0) Gecko/20100101 Firefox/96.0."
Different web browsers have different formats for this, and due to the way some user-agent parsing libraries work they may cause issues when reading three-digit major version numbers. For an in-depth read on what implementations cause this, look here.
Back in August 2021, Mozilla started an experiment to find out if three-digit version numbers could cause issues, and found that a small number of websites wouldn't display or work properly.
Notable examples including Yahoo, Bethesda, HBO Go, Slack, and more are added to the list every day. Google has a similar ongoing effort that allows developers to force the v100 user-agent string for testing purposes. This revealed that websites built with Duda wouldn't display correctly, but the issue was fixed in December 2021.
The good news is that Google and Mozilla are both working on ways to mitigate any potential issues that may arise, for example by freezing the major version to 99 and reporting it in the minor version part of the user-agent string.