Deleting the following folder solved the gap issue:
C:\Program Files (x86)\Mozilla Firefox\distribution\bundles\websitelogon@truesuite.com
Now the software is disabled in Firefox altogether, though. Here are the original contents of the folder:
https://db.tt/fHosAnV1.
If anyone is able to make HP SimplePass and Firefox 30 compatible without a gap in the address bar, I do have a PayPal account.