Persistence is essential. If We're talking of an extension, it is also necessary to pass persistence to the features not covered by the persistence of the core.

Check that in the "About" section the version and the build number are displayed.

Any functionality tested with persistence passes to the background. This means that We need to identify the features that are outside of persistence.

It is imperative to test the new functionalities, either they're on an extension or not.

Cases where a response or outcome is requested are a priority. Most of these cases use the OK button. Proving the case once with the Cancel button is enough.

If there are test cases alike try to generalize them into subgroups. That is, if we have the same test cases for different types, write the test cases without repeating the types.

If there are similar test cases with the same expected final result, we have to prioritize the most common of them.