See these articles for some suggestions:

• https://support.mozilla.org/kb/Firefox+has+just+updated+tab+shows+each+time+you+start+Firefox
• https://support.mozilla.org/kb/How+to+set+the+home+page - Firefox supports multiple home pages separated by '|' symbols
• http://kb.mozillazine.org/Preferences_not_saved

I was about to ask the same. FF just updated itself to 10.0.1, and now it keeps opening with http://www.mozilla.org/en-US/firefox/10.0.1/whatsnew/, in addition to whatever tabs I had open the last time. Meanwhile, my preferences are (and have always been) set so that it should open with a blank page and even my home page is set as "about:blank". This would seem to be a bug with the update process to 10.0.1.

If I look at about:config and search for "start", I see the following entries. No matter how many times I clear them and restart, they keep coming back:

browser.startup.homepage_override.buildID 20120208060813

browser.startup.homepage_override.mstone rv:10.0.1

startup.homepage_override_url http://www.mozilla.com/%LOCALE%/%APP%/%VERSION%/whatsnew/

I don't have multiple home pages listed and I reset the preferences to default. The issue didn't change; the FF start page and my home page still load every time I start FF. It's annoying.

It turns out that a restart of the machine will fix the problem. Restarts aren't usually required for Firefox updates, so this is probably a bug. But at least their is a relatively simple way of working around it.

I restarted my computer and the problem persists.

Edited to add: the 2nd time I opened Firefox after restarting the computer, the problem went away. How weird is that? But good enough, thank you.