"0x80004005 NS_ERROR_FAILURE [nslStringBundle.formatStringFromName]" error message on open

this is almost certainly triggered by some extension you have installed.

Start firefox without extensinos loaded by running from the command line:

  firefox -safe-mode

... if that helped, disable your extensions one by one in the tools -> addons dialog until your problem goes away.

Thanks,
  - Alexander

Removed extension forecast fox and error message has resolved itself. Thanks!

FYI, this problem appears to be caused by a permissions issue in your home directory. For instance, if you start Firefox by using "sudo firefox", some files in your Firefox profile directory will become owned by "root:root". To fix, run the following:

sudo chown -R $(id -u):$(id -g) ~/.mozilla/firefox/

Alternately, to avoid this problem in the future, be sure to use "sudo -H firefox" to set the root user's home directory before starting Firefox (disclaimer: you should avoid running Firefox as root).

to fix without disabling extensions, try running:

sudo chown -R $(id -u):$(id -g) ~/.mozilla/firefox/

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FOR ALL FIREFOX EXTENSION DEVELOPERS::
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The exception / the bug is trown / produced, if you have NON UTF8 chars - Special Chars eg.: ÄüöÜß ... within your .properties file

(cost me about 2 hours to find this out!)