Google toolbar is created by the Google Corporation and is not directly affiliated with Firefox. To put it in perspective, Firefox is like the grocery store, and google tool bar is like the milk. Firefox said "we are opening this new store" and google (the milk delivery guy) hasn't brought them any milk yet.

However, I hear-tell that it might have been updated in the past couple minutes, maybe give it another shot? https://www.google.com/intl/en/toolbar/ff/index.html

if not, I can't see it taking them more than a day or two to catch up.

I understand what you are saying. My point is Firefox should make a big point of warning people this new release may not yet be supported by 3rd party plug ins.

I would have waited to upgrade knowing that.

I know Google is not the same company, but the 4.0 Mozilla worked great with the google toolbar. Yahoo toolbar is not compatible either. I think they will come up with updated toolbars for both. I've had Google mail and page plus toolbar for at least 10 yrs.

The GTB 7.1.20110512W version works in Firefox 5.0 by using the Compatibility Reporter extension, I tried it myself due to the large number of postings about the GTB this morning.
https://addons.mozilla.org/en-US/firefox/addon/add-on-compatibility-reporter/

There are hundreds and hundreds of add-ons being created by individuals and it's unreasonable to expect Mozilla to make sure all add-ons are compatible before they release a new Firefox version. These add-ons were created by individuals and it's the responsibility of each add-on developers to update their product to make sure it'll work for future Firefox release, which, they have advance notice because of the beta versions of Firefox being released.

To fix the add-ons problems, you can use the-edmeister's suggestion or use the following instructions, which have worked for five of my add-ons:

http://kb.mozillazine.org/Editing_an_add-on_to_change_its_compatibility

For Google toolbar there is a quickfix for firefox 5.o See: A. Jooms post here: https://support.mozilla.com/en-US/questions/837142?s=Google+Toolbar+for+Firefox+5.0&as=s

Since Google is not exactly rare, it might have been wise to address the GTB issue before offering FF5. The loss of GTB makes Google Chrome look very good.

I think most understand that they are separate companies, but I've been using the updates for about a decade now and always get the notice that some add-ons won't be compatible. I assumed they meant that as usual some of my dictionaries and smaller add-ons had not been updated yet. Google toolbar, however, is so basic that it used to come together with Firefox when you downloaded it. If I had been given a way of knowing which add-ons weren't available, I would NEVER have downloaded this as I've now lost all of my bookmarks. Here's hoping they update it quickly, because I don't want to bother with the fixes I've now spent an hour researching.

@jjcadenza Keep using Firefox 5, it has better security. Google Toolbar still works just fine with Firefox 5, but until Google releases a toolbar compatible with Firefox 5, you need to disable add-on compatible versions verification. You can do this by installing Mozilla's Add-On Compatibility Reporter extension from https://addons.mozilla.org/en-US/firefox/addon/15003 and restarting Firefox twice. It basically tells Firefox to ignore the maximum compatible version so the toolbar can be enabled on version 5 too, not blocked just because Firefox releases major version numbers like mad just for the sake of catching up with IE9 and Chrome 12.