Finally got the Google Toolbar to install
I think the problem is with Fast User Switching & Firefox 3.
My wife has her own logon to our iMac & so do I.
The toolbar installed no problem for me, but I kept getting the "Firefox could not install the file at " error.
So based on the instructions below I created another Firefox profile for her & it installed without any problems.
Logged on as the user having problems, here is what I did:
http://support.mozilla.com/en-US/kb/Managing+profiles
Mac OS:
1. Exit Firefox. To close Firefox, in the menu bar, select the Firefox menu, and then select Quit Firefox.
2. Navigate to /Applications/Utilities. Open the Terminal application.
3. In the Terminal application, enter the following:
/Applications/Firefox.app/Contents/MacOS/firefox -ProfileManager
http://support.mozilla.com/en-US/kb/Managing+profiles#Creating_a_profile
To start the Create Profile Wizard, click Create Profile... in the Profile Manager.
Click Next and enter the name of the profile. Use a profile name that is descriptive, such as your personal name. This name is not exposed on the Internet.
You can also choose where to store the profile, which is useful if you plan on exporting your data and settings to another computer or setup in the future. To choose its storage location on your system, click Choose Folder....
Note: If you choose a custom location for the profile, store it in a new or clean folder. When you choose to remove the profile, all contents stored in the same folder are removed.
To create the new profile, click Finish.
The new profile is displayed in the Profile Manager.
Open Firefox.
Install Google toolbar
http://www.google.com/support/firefox/bin/answer.py?hl=en&answer=22027