How to open a local file from your computer
in Mozilla Firefox, posted Oct 26th 2011
If you're using the menu bar, to open a local file via Firefox the easiest way is to click, click "File" menu, and then select "Open File".
Alternatively, you can press the "Ctrl" "O" keys simultaneously; both of these methods open the "Open file" dialog. Simply select a file in this window, then click "Open".
Finally, it's also possible to drag & drop a local file on the browser's content window to open it.
If the opened file is an HTML file, it will behave just as if it is on a website. However, you can also open an image or text file to view it in your browser.