If the problem is with the add-on for the tor button itself it would be worth trying the compatibility browser add on.

(Donate ?), download, install, and run; the add-on from compatibility reporter

See also

• thread How do I over-ride Firefox 4's refusal to allow installation of Torbutton ...
• no doubt further info is available from Tor's own sites
  • https://www.torproject.org/torbutton/
  • https://www.torproject.org/index.html.en

No doubt someone has already solved this problem. Does the Compatibility Reporter solution I have suggested work ?

How can I enable Tor in Firefox 5?

1) Install "Stable Vidalia Bundle works with Windows 7, Vista, XP, https://www.torproject.org/dist/vidalia-bundles/vidalia-bundle-0.2.1.30-0.2.12.exe (sig)

2)In Firefox 5 "Tools" menu > "Advanced" toolbar > "Network" Tab > "Settings" button, follow the 1st image (Manual proxy configuration:) then the 2nd image (Auto-detect proxy setting for this network:) and then "Ok".

3) Be sure that "Tor" network is connected. Now you can install the "Torbutton" by selecting Install Stable:https://archive.torproject.org/tor-package-archive/torbutton/torbutton-1.4.0.xpi

Welcome to Tor in Firefox 5 :)

References:

http://support.mozilla.com/en-US/questions/769300

https://support.mozilla.com/en-US/questions/841707

• 1) Install "Stable Vidalia Bundle works with Windows 7, Vista, XP, Download Stable (sig)

The link contained in that is a direct download link, would it be better to give another link so that anyone using it could immediately see what was likely to download. Or at least give the raw link https://www.torproject.org/dist/vidalia-bundles/vidalia-bundle-0.2.1.30-0.2.12.exe

• "References: https://support.mozilla.com/en-US/questions/769300/edit/208039 "
  

"https://support.mozilla.com/en-US/questions/841707#answer-207433 "

The links redirect wrongly try
/questions/769300#answer-208039 &
/questions/841707
not sure why your links do not work the copies seem to ! maybe the originals contain some odd character. (The edit will only be available to yourself)