Works Fine In Safari, But Not In Firefox

I've installed Zen Cart on a PowerPC G4 and it's working great in Safari v3.1, but Firefox 2.0 can't locate the same http://localhost/store that Safari has no trouble with.

The way I did it:

1. Installed MAMP (XAMPP for Mac didn't work quite right)

2. Set default Apache and MySQL ports in MAMP (80 and 3306, respectively)

3. Set MAMP to use PHP 4 (in MAMP Preferences)

4. Created a new database using phpMyAdmin (also in MAMP Preferences)

5. Decompressed Zen Cart into the /MAMP/htdocs directory and named it "store"

6. Changed configure.php in the /includes directory to read-only

7. Went to http://localhost/store in my Safari browser and followed all the installation instructions for Zen Cart

Since then, I've been successfully perusing the chapters in the e-Start book, and got to a point where I wanted to see how things worked in Firefox, but it refuses to connect to the http://localhost/store directory. I've tried http://localhost:80/store and http://127.0.0.1/store but I only get the directory in my /Library/Webserver/Documents directory.

Is it possible that the local install will only permit the use of one (default) browser?

Any suggestions are welcome here...