Firefox doesn't close properly

I'm using FF 29.1 and am having a problem. When I close FF and want to open it later again about 75% of the time I'll get an error message. I have enclosed a JPEG of it below. I then have to open Task Manager and end the process by hand. FF will then open properly. I started having this problem before updating to V29. I use Win 7.
Any suggestions will be appreciated. It's driving me crazy.
Thanks
Floyd

 

See if you have an add-on or extension that is not closing properly. This has been the cause of some symptoms you're experiencing that sound familiar.

 

This is a known issue with FF 29.x + builds, refer to https://www.mozilla.org/en-US/firefox/29.0.1/releasenotes/
Fortunately, most people don't have this problem - just the lucky ones.