Rated 3 out of 5 stars

I cannot install this addon either,because of an error message: A better firefox addon bar cannot be installed because Firefox cannot modify the needed file.
I try to search in the Internet,I find that may be the answer:
https://forums.mozilla.org/addons/viewtopic.php?f=27&t=3471
It seems that some intermediate file of the installation process is being created with a name longer than the maximum supported length and then the installation process fails.

Your add-on name may be too long in the internal.

Dié resensie is oor 'n vorige weergawe van dié byvoeging (1.1.1-signed). 

Cannot modify the needed file fix

Please go here to find the solution to your problem, http://support.mozilla.com/en-US/questions/818704

If you are still having problems, leave me a comment here:
http://indexedout.blogspot.com/2011/11/better-firefox-add-on-bar.html

Also let me know if there are any other details related to the error you are experiencing, thanks!