Manual:$wgBrowserBlackList

Details
Browser Blacklist for unicode non compliant browsers. Contains a list of regexps : "/regexp/" matching problematic browsers. If the user-agent of a browser matches one such regex, the "safemode" field is used when editing (see the  item in Manual:Parameters to index.php for details).

Current version
From some later version of MW than 1.7.0, this setting had the following default values:

The changes between this and the previous version are:
 * There was a change to regexes for Netscape 2-4 detection.
 * The Google Wireless Transcoder regex was added.

1.7.0
From 1.7.0 until it was changed to the current version (we've not yet figured out when this was...), this setting had the following default values:

Prior to 1.7.0
From 1.4.1 to 1.6.10, this setting had the following default values:

Prior to 1.4.1
In 1.4.0, this setting had the following default value: