After I close Firefox, it will not open again unless I restart my computer.

Question

When I close Firefox normally, I cannot open it again unless I restart my computer. Why?

Answer 1

Yes, that is a strong indication that Firefox didn't close completely.
You can check that in the Task Manager (Ctrl+Alt+Del).<br />
If you see Firefox and plugin-container processes then you can close (kill) those processes and you should be able to start Firefox after having done that.
There are other things that need your attention.
Your system details list shows that you still have a very old Flash 9.0 r45 plugin installed that you should remove.
*Shockwave Flash 11.7 r700
*Shockwave Flash 9.0 r45
This plugin might be installed in the plugins folder in the Firefox program folder.
*(32 bit Windows) C:\Program Files\Mozilla Firefox\
You can set the <b>plugin.expose_full_path</b> pref to true on the about:config page to see the full path of enabled installed plugins on the about:plugins page.
*http://kb.mozillazine.org/about:plugins
See:
*http://kb.mozillazine.org/Issues_related_to_plugins#Identifying_installed_plugins
You can open about:xxxx pages via the location bar like you open a website.
*http://kb.mozillazine.org/about:config
It is best not to leave that pref set to true as it exposes that full path to web servers via the navigator.plugins object, so reset that pref to its default value false after you are done with the about:plugins page and have located the old Flash plugin.
See "Manually uninstalling a plugin":
*https://support.mozilla.org/kb/Troubleshooting+plugins