Firefox, like some other popular web browsers, allows you to open PDF file using an internal viewer. But this internal viewer cannot handle all sorts of PDF files. Some of the PDF files have special features that can be used if opened in a full featured PDF viewer like Adobe Acrobat or Foxit Reader. You can use the pdfViewerSwitcher extension to switch the PDF file between internal viewer and the Adobe Acrobat plugin in Mozilla Firefox.
You can install the pdfViewerSwitcher extension from the Mozilla add-ons website. The installation of this add-on does not require you to restart the web browser and it can be used immediately after the installation. After the restart, you will see a new Adobe Acrobat icon in the addon toolbar near the lower-right corner of the Firefox window.
If this icon is grayed out, then it means that you have not installed the Adobe Acrobat PDF viewer add-on in the Firefox browser. You can install this add-on when you are installing Adobe PDF viewer in your PC. Clicking on this icon would switch the PDF viewer to Adobe Acrobat and open your PDF file in it. Clicking on this icon once more would switch the PDF viewer once again to the Firefox internal PDF viewer.
Sometimes when you have come across interactive PDF files in which you have to fill up information before taking the print out, or saving the PDF file and re-upload it, among many other things. For all such activities its better to open the PDF files in full featured PDF viewer applications like Adobe Acrobat. The pdfViewerSwitcher enables you to switch between the internal viewer and the Adobe PDF viewer at will.
You can download and install the pdfViewerSwitcher add-on from https://addons.mozilla.org/.