Please click the orange Firefox button, go to Add-ons, then Extensions. Can you see it in there? If you can see it, make sure it's enabled.

If it's not in the Extensions manager, reinstall it.

If it is visible and enabled, do the following.

1. Right click a blank part of the Tab bar and then click Customize.
   
   
2. In the panel which opens, look for the ForecastFox button and if you find it, drag it onto the toolbar (along with anything you think might be useful)
   
   
3. Click "Done" to exit.
   
   

If this answers your question, please click the Solved it button next to this post after you log in into the forum. This will help others searching for a solution to the same subject.

Thanks.

Done, and done; it was enabled and installed. I removed and reinstalled it for good measure.

This is what I have in Customize; I can see other items, but not for Forecast Fox.

What a stupid way of doing things in this extension! I have been using Firefox since 2002, have used or tried many hundreds of different extensions, and it took me almost 10 minutes to figure out how it works.
No help here - http://www.getforecastfox.com/ - and the picture is for a Mac, which is like what, 5% of the Firefox user "market".
And their "support" - Questions? Need help? - http://groups.google.com/group/forecastfox-users/ - shown on the download page, has very few "answers", mainly a bunch of questions by lost users.

The ForecastFox display is on the Menu Bar, which is hidden by default in Firefox 4.0 and later versions on most OSs, except for WinXP - but it should appear when the Customize mode is open, whether Tabs on Top is selected or not. (I have no idea why it doesn't appear in your screenshot.) You can also see it if you hit the Alt key, then you need to open View > Toolbars and click on Menu bar to have it open all the time.

Plus there are no instructions on how to configure and use this extension, and isn't easily discoverable - they should be using a "first run" page set to the forecastfox Options page with some sort of instructions and screenshots for all the operating systems.
http://www.getforecastfox.com/customize/16/ - for changing Options, like adding a "location", changing "units", etc. And the "button" for "customizing" or moving the display only appears when that page is loaded in Firefox, even in a tab that isn't showing! ( And that brings up a security concern with Firefox, because that isn't a "secure" page, but that's something I'll bring up in the Addon's support fora or at Bugzilla.)

The "display" can be moved to a different Toolbar, but you need to have the Customize mode open and "drag" the + with the circle around it (which only seems to be present when this - http://www.getforecastfox.com/customize/16/ - page is loaded in Firefox), to be able to move the display to a different location. Also, a distinct lack of "convention" with customizing, it's using cursor changes that aren't the same as with the other 10's of thousands of Firefox add-ons that are available for Firefox. A "hand with the index finger extended" is the usual cursor used for showing the "sweet spot" for "drag" in Customize mode, but this extension uses the "move" cursor instead - the Tooltip for that "move" says -
" Drag and drop to move Forecastfox.
Close the options page to hide this icon."

See CSS2 Cursor properties - http://www.gtalbot.org/DHTMLSection/Cursors.html

I hope this answers all your issues with the Forecastfox add-on.
https://addons.mozilla.org/en-US/firefox/addon/forecastfox-weather/

I just installed the Add-on on my own system and all the buttons on the right of the screenshot appeared immediately. So I think that if that didn't happen with your own installation, then you you may have a corrupt localstore.rdf file.

See this article for instructions on how to fix the problem: http://kb.mozillazine.org/Corrupt_localstore.rdf

Thank you, the-edmeister, you nailed it!

You're welcome.

I filed a Bug report about the issue of what I consider incomplete instructions for that add-on on the AMO website. But as I suspected would happen when I was filing that report, it was marked as INVALID.
https://bugzilla.mozilla.org/show_bug.cgi?id=675108

I even did a review of that extension to alert other people to this "problem" and direct them to this thread for help, and wouldn't you know it, the next review is about the same thing - "I have the addon installed but I don't see it anywhere".

It's a shame; for the most part it's an decent addon, the documentation just needs work. Thank you for your efforts.