[MacTUG] FireFox 19 includes a built in PDF viewer

[Dani Roloson]

So I've update MFCF documentation to read:

10.6 through 10.8

Firefox 19 and higher includes pdf.js.
Also go into Tools -> Add-ons and disable Adobe Acrobat NPAPI Plug-in, the Schubert plug-in, and PDF.js since that isn't the built-in one (i.e. anything that would try to handle PDFs instead).

10.5

Firefox 16 is the last version of Firefox that works on Mac OS X 10.5
(Leopard). We should be replacing those machines since 10.6 came out
June 2008.