Information has been posted for repairing most Firefox versions old and new.

https://support.mozilla.org/en-US/questions/1258165#answer-1218833 fixed the issue for my v54.

Did you enable "Resist Fingerprinting" (troubleshooting data shows: Firefox 60 ESR on Windows 7)?

You can check this pref on the about:config page to see if resist fingerprinting (RFP) is enabled and if this pref is user set (bold) reset to false via the right-click context menu.

• privacy.resistFingerprinting = false

See also:

• https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting

There has been an unfortunate incident with an intermediate certificate that had expired recently and this certificate was used to verify the signatures of extensions hosted on the Add-ons website. This expired intermediate certificate caused Firefox to distrust and disable all installed extensions. There have been Firefox updates released to address this issue (66.0.5 and 60.6.3 ESR).

• https://support.mozilla.org/en-US/kb/update-firefox-latest-version

Although change can be understandably frustrating, updates are an important part of staying safe when browsing the internet. Updates contain fixes for hundreds of security and privacy flaws, not to mention great features that are added.

<strike>In your case, the plugins stopped working because Firefox no longer supports NPAPI plugins. Plugins are a massive security risk and performance hindrance. None of the major internet browsers support this outdated technology anymore.</strike>

EDIT: The user is likely referring to extensions, not "plugins".

Wesley Branton said

In your case, the plugins stopped working because Firefox no longer supports NPAPI plugins.

The OP was very likely referring to Extensions.

The Flash Player Plugin from Adobe has been the only NPAPI Plugin allowed to run since Firefox 52.0 Release.

Though the Flash Player Plugin (NPAPI) will be allowed under increasing restrictions over time. https://developer.mozilla.org/en-US/docs/Plugins/Roadmap