If you want to know the compatibility of latest Firefox with your older addons, or updated addons with older browsers, use this extension called Addon Compatibility Reporter. This ensures Mozilla whether it has issues with alpha and beta releases.
If you will finish the installation of Addon Compatibility Reporter, your compatible extension will be enabled for you to test whether they are able to work with the current Firefox or Thunderbird. If you come to know that one of you’re addons is not working with the latest version, go to Addons Manager and click Compatibility next to that addon in order to send a report to Mozilla.

If you get incompatible report and your addons are still working well, please let Mozilla know that they work fine by submitting a success report, so Mozilla can encourage the add-on developer to update their compatibility information. Moreover, if you don’t want to use this addon, you can revert back the browser to the previous settings.

From