In Firefox and Thunderbird, add-ons (extensions and themes) can be updated using the Software Update feature. To perform an update check:
- Firefox and Thunderbird: "Tools -> Add-ons -> Find Updates"
Settings to automatically check for updates to installed add-ons are found under "Tools -> Options -> Advanced -> Update" in Firefox and Thunderbird and under "Edit -> Preferences -> Software Installation
Updating incompatible add-ons for a new application version
The Add-ons dialog will inform you if an existing add-on is incompatible with the current version of your application. Thunderbird will also disable the add-on and prevent you from enabling it by right clicking on the add-on in "Tools -> Add-ons" and pressing the enable button. The first thing to try is to check for updates to see if a new version is available. If one isn't found, you can override the compatibility check. Most add-ons will work if you do that, but it can cause the application to behave improperly. If that happens disable or uninstall the extension from the Add-ons dialog (from Safe Mode if necessary).