Firefox works fine on version 26. When it updates to version 27, i get undefined entity. I've tried getting profile manager to run and it won't. Need help

Question

Version 26 works fine. When it updates to version 27.01, I get undefined entity. I've tried uninstalling and then reinstalling. I've tried to bring up profile manager but it doesn't come up. I've tried deleting Firefox folders. I'm very disappointed that Firefox rolls out an update that causes problems. None of your recommendations is working and I really hate to lose Firefox but this is pathetic. I'm using version 26 as much as i can till someone gives me the right solution. Is there a simple link to click on that will clear up any old profiles and simply fix this issue?

Answer 1

That means you need to clean reinstall.
Certain Firefox problems can be solved by performing a ''Clean reinstall''. This means you remove Firefox program files and then reinstall Firefox. Please follow these steps:
'''Note:''' You might want to print these steps or view them in another browser.
#Download the latest Desktop version of Firefox from http://www.mozilla.org and save the setup file to your computer.
#After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu).
#Delete the Firefox installation folder, which is located in one of these locations, by default:
#*'''Windows:'''
#**C:\Program Files\Mozilla Firefox
#**C:\Program Files (x86)\Mozilla Firefox
#*'''Mac:''' Delete Firefox from the Applications folder.
#*'''Linux:''' If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see [[Installing Firefox on Linux]]. If you downloaded and installed the binary package from the [http://www.mozilla.org/firefox#desktop Firefox download page], simply remove the folder ''firefox'' in your home directory.
#Now, go ahead and reinstall Firefox:
##Double-click the downloaded installation file and go through the steps of the installation wizard.
##Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.
More information about reinstalling Firefox can be found [https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems?esab=a&s=troubleshooting&r=3&as=s#w_5-reinstall-firefox here].
Please report back to see if this helped you!
Thank you.