[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Start Firefox in Safe Mode] {web link} A small dialog should appear. Click '''Start In Safe Mode''' (not Refresh). Is the problem still there?

Tried to open in safe mode. Even that behaves the same.

Let’s do a full clean re-install; Note: Firefox comes in three or more folders on all computers. They are; Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user. If you remove the Firefox folder, the user profiles would not be affected. ----------- [http://www.mozilla.org/en-US/firefox/all/ Download Firefox For All languages And Systems] {web link} Save the file. Then '''Close Firefox. ''' Using your file browser, open the '''Programs Folder''' on your computer. '''Windows: ''' C:\Program Files C:\Program Files (x86) '''Note:''' Check Both Folders '''Mac: ''' Open the ''' "Applications" ''' folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac '''Linux: ''' Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any '''Mozilla''' or '''Firefox''' program folders. Do not remove the '''Mozilla Thunderbird''' folder if there is one. '''Do Not''' remove any profile folders. After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your '''Computer''' in safe mode and try again. http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

I've had a similar problem, but did not think directly the same, reported here: https://support.mozilla.org/en-US/questions/1285436 During my testing, I now think it's likely the same issue. I've submitted a bug, details found here: https://bugzilla.mozilla.org/show_bug.cgi?id=1638675