And: both of us downloaded Zotero from Zotero.org, not from Mozilla.

I have no "tools" menu that I can see in Firefox (saw those instructions you linked in my own search for a solution and this stopped me there)

If you have no Tools menu, either you're not using Firefox or something is seriously wrong with your installation.

Also, checking the Incompatible Extensions list isn't enough. You have to try disabling all your other extensions.

Yes, I am using Windows 7.

But even for Windows 7, the zotero button ought to appear in the lower right, assuming one has the add-ins toolbar showing so I guess we're still talking corrupt extension files, right?

So I did everything that it says for corrupt extension files and it still has not appeared.

It freezes the browser every time I click options for Zotero(when I'm at the extensions list). If I were to uninstall and reinstall Firefox would that erase everything that I have in Zotero. This is really giving me a difficult time. I don't won't to lose all of my information.

But no, uninstalling Firefox won't erase your Zotero data unless you choose the option to erase your profile, which is not the default.

You should try reinstalling Firefox.

Beyond that, check permissions on your Zotero data directory.

If it's still not working, see if you can generate real-time debug output for Firefox startup.

If you don't want to take the time to debug this, you can always just download Zotero Standalone. When it first starts up it should ask if you want to use the existing Zotero for Firefox data directory. If you say yes, it should open your library (assuming there's not a permissions problem with your data directory or a problem with your hard drive). If you say no, you can transfer your library to Zotero Standalone's default data directory location.