From MozillaZine Knowledge Base

Highlight Color

Re Accessibility_features_of_Firefox#Begin_finding_when_you_begin_typing, the way to change the highlight color should be documented.

Issue is also documented at http://forums.mozillazine.org/viewtopic.php?f=38&t=1331845, at which time the settings were at about:config - > ui.textHighlightBackground ui.textHighlightForeground ui.textHighlightForeground ui.textSelectBackgroundAttention and so on, but these don't appear to apply in Firefox 3.x.

Per http://www.neowin.net/forum/topic/284675-firefox-highlight-color/ it used to be at about:config - > ui.textSelectBackground, which also doesn't appear to apply in Firefox 3.x.

I can't take much more of this purple color which appeared all of a sudden.