Evangelism/UA Date Change Letter
Here is a sample letter. You need to replace the site URL, bug URL and signature.
Title: Site Broken in Upcoming Firefox Release
I am a Mozilla project contributor, and I need to report to you that your site:
is broken in an upcoming release of Firefox. Firefox has about a 20-25% market share across the world, and so I'm sure you are keen to make sure that your site keeps working for Firefox users. The good news is that we know what the problem is, and it's probably not hard for you to fix.
Firefox 17, due for release around 19th November, has changed its User Agent String from (using Windows 7 as an example):
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20100101 Firefox/17.0
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/17.0 Firefox/17.0
Testing has shown that Firefox works fine with your site with the old string, but does not work with the new string. We therefore presume that you are detecting particular strings or parts of strings and making decisions based on that. You need to immediately update your detection logic to recognize the new string, and then Firefox will continue to work.
In general, we would suggest that User Agent sniffing is a bad way of detecting anything. New standards-compliant browsers appear all the time (for example Yandex, the biggest search engine in Russia, just launched one), and we ourselves reserve the right to make changes to the string in future. You are much better off doing specific detection for the features your website needs to function correctly. We would commend to you our documentation on writing forward-compatible websites, in particular the section on Sniffing: https://developer.mozilla.org/en-US/docs/Web_development/Writing_forward-compatible_websites
This issue is tracked on our bug system here: <bug URL>
With best wishes,