First Try start Firefox in Safe Mode, sometimes this problem is caused by addons: *[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Firefox in safe mode] Also scan your PC, can be malwares the problem: *[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware Problems caused by malwares] Also: *[https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem Create a screenshot of the problem]