If you're using Firefox 3 to browse the Web, you may have noticed that it's missing one essential feature (for many) that you can find in Safari: you can't view PDFs in a browser window. When you click a link for a PDF file, Firefox 3 downloads the file, forcing you to then open it in Preview or Adobe Acrobat Reader.
Well, there's now a Firefox extension named firefox-mac-pdf, available for Firefox 3 that utilizes the built-in PDF support in OS X to display PDFs in the browser.
This extension doesn't have the nifty fading bezel that the Safari PDF viewer does, but it supports all the same keyboard shortcuts and you get the standard Mac OS X PDF contextual menu when you control-click on a displayed PDF.
"View Inline PDFs in Firefox 3" Comments