“custom_domain is null”error message in Firefox

Problem: When opening a “localhost” address using Firefox, a JavaScript error message is displayed with the error message “current_domain is null”.

Description: Using Firefox version 3.0.11. Error message only appears when connecting to a site hosted on the local machine. Disabling all add-ons resolves the problem. Re-enabled add-ons one by one. Re-enabling LongURL Expander causes the problem to re-appear. Error message is known issue with version 2.0.0 of the add-on.

Solution: As per the comments on the the add-on page, edit the longurlmobileexpander.js file to make the requirement for the second part of the domain name optional.

On Mac OS X, open home folder and browse to Library/Application Support/Firefox/Profiles/[profile].default/extension/{a7101e54-830c-4d33-a3ed-bedc17ec44da}/content
Open longurlmobileexpander.js in TextEdit.
Edit line 78 to read:

var current_domain = document.location.href.match(/^https?://(?:www.)?([^.]+(.[^/]+)?)/i);

Save changes.

Thanks to Mathias Jansen for the solution.