I have been using Firefox for many years and never had issues. Two days ago, I turned on my HP with Windows 10 and I got a pop up message something about Error Platform 126.0 XUL Runner is not compatible. I could not access Firefox, Google, or the internet. I uninstalled Firefox and reinstalled, but after that, everything runs very slow. Each time I go into a website, it can take up to over a minute to pull up! I cannot even delete email from my Gmail! It's piling up. Downloading can take over an hour! I checked all the trouble shooting forums in Mozilla and tried just about everything. I went back into "About:profile"s and created a new profile. It it did not make any difference. I also did a Firefox refresh. Did not help any. I went back into the profile I had before the XUL error because my bookmarks were there. Still slow. I cleaned out the cache, in both Firefox and my Windows 10. made no difference. I only have three extensions in Firefox. I don't know what else I can do to fix this. Also, my drivers and other software are automatically updated by Windows. My HP is only 2 years old as well. Everything was fine in Firefox until that XUL error message popped up and I had to uninstall and reinstall Firefox. That is when everything became agonizingly slow!

Update: My computer is barely usable anymore because of the Firefox issue. Having to wait for a minute or more for everything I do on the internet? I know it cannot be my computer itself because it is not even two years old yet. I may have to dump Firefox if I cannot get this fixed. I have Norton 360 and it is not malware or a virus. Firefox messed something up.