Initially Firefox would not start saying that the xul.dll could not be read by windows or was corrupt followed immediately by xpcom.dll could not load. Researched your website and re-installed Firefox as per instructions, deleting the Mozilla directory in Program FIles as directed. This worked and Firefox came up and worked fine but after I closed it and shut down for the night and started up the next morning, the same problem appeared. I once again re-installed Firefox [v27.01] as instructed and it worked fine but once again this morning it failed to start with the same error messages. This is now a recurring problem making the program unreliable and forcing me to use a competitor's product, even to request this support. Can you help? Peter W.