Usually on Firebug, when inspecting an element, I get a list of fonts, and will actually need to go to the system's Fonts folder and check the names one by one to see if that's the one being used. Is there a way to show the font being used directly using Firebug?
Or if Firebug doesn't have this feature, can any other add-on do that?
In firebug on the HTML tab you can inspect the dom node css properties too. If there isn't any font-family declaration, then it uses the default.
No, all you get is the list. The list functions as a fallback mechanism. If the first font is unavailable, the second will be used and so forth. I would recommend, if you're just trying to work out which font is being used in a specific scenario, that you use firebug to muck about with the font style, reducing it to the last single font in the list. Then add the additional fonts to the list, one by one and see if the font changes on the page. If it doesn't change, you're missing that font.
You can edit the list of fonts on the font declaration in firebug.
Starting from the first font, I stick an 'x' in the name. If the font on the page changes, that was the one used.
If it doesn't, I go down the list renaming the fonts until one changes or I get to the default.
There is no way, programmatically, to determine which font is used when a web page is being viewed.