A small number of add-ons may be listed as unsupported or may not appear in about:addons. Their data is not lost; users should be able to re-install the add-ons and recover the data (Bug 1549129). More support information

If add-ons that use Containers functionality (such as Multi-Account Containers and Facebook Container) were disabled as part of this problem, any lost site data or custom configurations for those add-ons will not be recovered by this release. Users may need to set them up and login again in about:addons (Bug 1549204). More support information

Themes may not be re-enabled. Users may need to re-enable them in about:addons (Bug 1549022). More support information

Home page or search settings customized by an add-on may be reset to defaults. Users may need to customize them again in about:preferences or about:addons (Bug 1549192). More support information