Erratic firefox behavior

[Jim Byrnes]

Using Ubuntu 12.04 firefox from the repositories updated to version 31.0

I'm not sure exactly when it started but for sometime now Firefox has 
been sometimes been starting up and opening whatever tabs I happened to 
leave open when I shut it down. I don't have any tabs pinned and in 
settings I have the startup page as about:blank.

I looked through about:config and found the following settings, which 
all seem to be correct.

browser.startup.page;0
browser.startup.homepage_override.mstone;31.0
browser.startup.homepage_override.buildID;20140715215003
browser.startup.homepage;about:blank

If I remember correctly there once was a setting that said not to reopen 
tabs that were open at shutdown, but I can't seem to find it now.

It appears to be random.  I can shutdown with tabs open 5 times in a row 
and have open a blank page and then the next 3 times it will open what 
happened to be open at shutdown.

Due to the randomness of the problem it could be a long time consuming 
process to start disabling addons or setting up a new default profile. 
So before I do that, I was wondering if anyone else was seeing this 
behavior and maybe had a solution.

Regards,  Jim