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). 

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!