Firefox 15 includes an all new PDF reader built into the browser–for those of you wondering, that means you can finally disable the Adobe PDF Plugin and uninstall it once and for all.
Note: obviously if you need to access more advanced PDF features, you’ll still need the Adobe plugin. For most of us, however, the built-in viewer is fine, or you could download PDF files and read them in the offline Adobe Reader.
Enabling Firefox’s Built-in PDF Reader
Open Firefox and navigate to about:config.
This will bring up a sarcastic warning telling you that you might void your warranty, just click the “I’ll be careful, I promise!” button to move on.
Now you will need to search for:
When you find it, right click on it and select Toggle from the context menu.
Next you will need enable the actual PDF Reader feature, you can do this by searching for:
That’s all there is to it, you can even drag PDF files on your local machine on t0 the Firefox windows to view them!
Note: As pointed out in the comments, you will need to disable the Adobe addon after you have completed this.