Hey Stanley, If you want someone to be able to give useful advice, I think you might have to provide a little more info. First of all, whether your computer runs well on XP is irrelevant, my "Windows 7 computer" also has full drivers for XP and Vista - so what? If you're not using XP, don't need to bring it up, lol. First of all, what do you mean by "local files", are you dragging and dropping videos or images into firefox to view them? Or is it something like a saved website? Here's something you can do: download a png image from Google (it can be anything, png, jpg, bmp, but not "webp", or just find a picture file somewhere, save a copy of it to your desktop. Then, hold the shift key on your keyboard, and use the mouse to "right click" the file on the desktop - a menu should pop up, and look closely, one of the options should be called "Copy as path", click on this normally with your mouse. (If you can't see "copy as path" as an option, it means you didn't hold the "shift" key, try again). Once you're sure you've clicked "copy as path" for that picture, you can open a blank notepad document, and press "ctrl" and "p" together to paste the image into notepad. Make sure it's a path that points to the image, you can tell by reading the path. Next, open a new tab in firefox, go to the address bar, delete everything, and press again "ctrl" and "p", to paste this path into the firefox address bar. Then press the "enter" key. What exactly happens at this stage? Pay close attention when you do it, so you can try to understand. If there is an error message or something, don't close it, but try to take a picture using the "print screen" button on your keyboard - then open Paint, and again press "ctrl" and "P", you should get a picture of your screen, make sure that picture contains the error message, save it and upload it somewhere (imgbb.com), (fastpic.org), or even (imgur.com), send us a link to the picture on here. Sorry I explained it very thoroughly just in case.