There is a legacy system in place that MAY allow extensions that are not 1.5 compatible to continue to operate. However, we strongly recommend that you update to the current version of all extensions prior to migration and that you check each extension's home page for specific recommendations about migration for that extension.
It is very wise to use a staging server or test server to try out extensions before deploying them on a production server.
There is no guarantee that all extensions will work.
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