An issue on the AOL’s Web mail service was reported that Firefox had been fallbacked to the basic application with limited features if the old build date (
Gecko/20100101) was not contained in the user agent (UA) string. Mozilla has contacted the webmaster to ask to fix the issue but got no response, so as an immediate workaround, Firefox has implemented a mechanism that can override the UA string for each site and applied that to
aol.com. Specifically, the value of a hidden preference
general.useragent.override.aol.com has been set to
Starting with Firefox 4, the UA string of Firefox has sometimes been made minor changes. When you detect browsers, you’re recommended to adopt a feature detection approach to see whether specific features (e.g. objects and functions) are implemented, instead of sniffing UA strings that are subject to change.