You have quite a few extensions installed. Did you check for issues caused by them? https://support

You have quite a few extensions installed.

Did you check for issues caused by them?

https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Do you otherwise have a problem with session restore?

You can check browser.sessionstore.* prefs including browser.sessionstore.resume_from_crash on the about:config page and reset browser.sessionstore prefs that are user set (bold) via the right-click context menu to the default value to make sure that Session Restore is enabled and working properly.

http://kb.mozillazine.org/Session_Restore

https://support.mozilla.org/kb/restore-previous-session

http://kb.mozillazine.org/browser.sessionstore.resume_from_crash

In case you are using "Clear history when Firefox closes":

do not clear the Browsing History

Tools > Options > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings

https://support.mozilla.org/kb/Clear+Recent+History

Note that clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, passwords, and other website specific data.