Looks like a Firefox problem Rated 5 out of 5 stars
I had installed this on Firefox on my work laptop 1-2 weeks ago and it has been working beautifully on that since then (that is why 5 stars). But now I tried to install it on my home laptop and got that same error message "This search engine isn't supported by Firefox and can't be installed".So according to the Firefox message I guess it is Firefox that is not supporting this (I have Firefox 3.6.12). Which is why I am keeping my 5-star rating.
By the way this reminded me of something funny I had often wondered about, that how come "Google" was always displayed on the top of the entries in my address bar dropdown? A couple of days ago I had removed all "Google" specific entries from the about:config settings and after this removal Google sites (such as www.google.com) no longer get saved to the address bar dropdown at all. Weird huh? Made me wonder if Firefox somehow called some functions on a google server when determining what to show in the address bar dropdown.By the way an earlier review had the suggestion to install Bing from:http://mycroft.mozdev.org/search-engines.html?name=bingThis suggestion works very good - at that URL, click on one of the many Bing links and answer Yes to the browsers question about adding the search engine.