Add-on signing is a verification process by Mozilla that helps to prevent users from downloading legitimate add-ons that may damage the user's system. Submitted add-ons go through a verification process. In version Firefox 48.0, the xpinstall.signatures.requried entry was disabled. This entry was never intended to be a permanent solution, but rather a workaround for users while add-on developers worked to get their add-ons to comply with the Mozilla policies.

For security reasons, is it highly recommended that you do not use older versions of Firefox because they may contain certain security flaws and don't contain the latest technology. However, Mozilla has archived every version of Firefox on their FTP server.

If you tell the developer of the add-on to get the add-on signed by Mozilla, they will probably do it, so it's a good idea to contact the developer.

I have read all of that about the add-on signing. The question was HOW DO I INSTALL A PREVIOUS VERSION OF FIREFOX SO THAT I CAN OVERRIDE THE 'XPINSTALL.SIGNATURES.REQUIRED' ENTRY.

THANKS

GENE

What is the addon you use ? There are probably alternatives that are signed, or maybe there is a good reason that particular one is not signed and it is dangerous or harmfull.

Instead of installing an older version to use in your ordinary browsing keep the current Release and install the third party Firefox portable ESR as an additional browser and use that just when you need the potentially dodgy add-on. That is NOT an official Mozilla Firefox suggestion because it is a third party build of the software, and the Firefox version is not intended for individual personal use, however it is what I may consider if in your position.

• http://portableapps.com/apps/internet/firefox-portable-esr

In answer to your direct question

If you want to increase the risks to your Data, Identity, System, and even potentially your money {if you make financial transactions on Firefox) then use an old unsupported version of Firefox see

• Install an older version of Firefox
  • Be aware of mozilla.org/security/known-vulnerabilities/firefox

If you do use an old version of Firefox remember once security holes are fixed and publicised the bad guys will target those that do not upgrade. To mitigate such risks consider precautions such as using a VM &/or having well rehearsed bare metal recovery plans.

P.S. There is other alternatives, aimed at Developers

• Add-on signing in Firefox_what-are-my-options-if-i-want-to-use-an-unsigned-add-on-advanced-users

However I am aware of either glitches or misunderstandings over updates and updates policy on the unbranded versions. (Personally I do not use or need them I always have at least Developer Edition available)

OOPS Sorry I just noticed you said it is an add-on from your Company. The obvious actions may be to contact the Company IT department. They can easily get the add-on signed.

• Add-on signing in Firefox

  Developers: To learn more about add-on signing guidelines, see Signing and distributing your add-on and Review Policies at Mozilla Developer Network.