The Yahoo Toolbar for Firefox is actually a lot older than the Google one...

I've just read the post at Slashdot:
http://slashdot.org/articles/05/07/21/2053253.shtml
"Yahoo Releases Firefox Toolbar Beta"

but in February Yahoo! announced this new tool
http://www.ysearchblog.com/archives/000077.html
"Firefox Got Yahoo!"

I think Dominik is right. Yahoo's Toolbar is older than Google's.

Phillip even posted about it when it came out:

http://blogoscoped.com/archive/2005-02-10-html#n41

Gee
That was about to happen :)