Is Firefox crashing?
If so, please submit a few recent crash reports. This will provide us with more details that we will need to solve the issue.^{Further Details}

Please take the following actions as well:

• Clear all cache and cookies ^{Further Instructions}
• Ensure all Firefox plugins are up-to-date ^{Check Now}

Please report back soon.

Have you have tested the same site in Safari to see whether it stays online while you are away? This would be helpful in determining whether to focus internal Firefox issues or to consider Mac OS issues as well.

If you connect to the site using a proxy server, private VPN service, or TOR, it's possible that your IP address is changing. Some sites like Yahoo cross check your IP address to prevent others from hijacking your session, and require you to enter your password again if it has changed. I think problems have also been noted on AOL network sites such as Huffington Post.

To check your connection setting, you can use this dialog:

(Mac) Firefox menu > Preferences > Advanced > Network mini-tab > "Settings" button

The default setting is "Use system proxy settings" but you might also try "No proxy" to see whether that makes a difference.

Details like websites remembering you (log you in automatically) are stored in a cookie.

• Create a cookie 'allow' exception to keep such cookies, especially in case of secure websites and when cookies expire when Firefox is closed.
• Tools > Options > Privacy > Cookies: Exceptions

It is possible that the cookies.sqlite file that stores the cookies is corrupted if clearing cookies doesn't work.

Rename (or delete) cookies.sqlite (cookies.sqlite.old) and delete other present cookies files like cookies.sqlite-journal in the Firefox profile folder in case the file cookies.sqlite got corrupted.

• http://kb.mozillazine.org/Cookies
• https://support.mozilla.org/kb/Deleting+cookies

That's Old flash make the problem

REMOVE OLD FLASH PLUGIN by some uninstaller app works.

I just have the same problem some days ago. I have searched for solution but no luck. But from that I have tried firefox have no problem in safe mode.

So I open my uninstaller program (in my case IObit uninstaller, but beware it will ask you to install bloatware, be sure to unclick it).

IObit Uninstaller > Toolbars & Plug-ins > Firefox > Scroll down to Plug-ins

check if there are old outdated Flash version remains.

If YES, uninstall them > Restart Firefox

In my case, all crashes gone.