The Web browser toolbar was for many years the way that expert researchers improved their Web browser. It provided nice added features (term jumping, highlighting) and saved search history. Google had one, Yahoo! had one, in fact nearly everyone who could do so created one. Some were little more than advertisements. Then the Web browser changed, as search began to be built in to the Web browser itself, usually as a box beside the location bar (where you type in http://www….). Then it shifted again. Why have two boxes, when you can search from the location bar? Google Chrome, Mozilla Firefox, and Microsoft Internet Explorer all support that now.
It was unsurprising, then, to see that Google will no longer be updating its Google Toolbar for Mozilla Firefox. You can still get it for Firefox or for Microsoft Internet Explorer. As with Realtime search, Google is paring down its offerings. Firefox is a superb browser and I expect all of the functionality the Google Toolbar provides is available by select Firefox extensions.