Thumbnails for .mov and .mp4 crashing after Windows updates

It won't be the Movie plugin itself; it will be one of the codecs/splitters installed on your system that handles MOV files.

(The Movie plugin knows nothing about .MOV files itself. It just acts as a gateway between the viewer and whichever codec/splitter DLLs are installed on your machine and registered against the different video types.)

This guide has some suggestions for fixing codecs/splitters:

Alternatively, disabling the Movie plugin is fine if you find other plugins work better. You'll probably have the files drop through to the ActiveX plugin which would then use Windows Media Player to display the files in the viewer pane. It may be using the same codecs/splitters, but in a way that doesn't upset them. (It also keeps things isolated in a separate process so if they do crash it won't usually take Opus with it. It also uses the 32-bit versions of the codecs/splitters by default, which are sometimes better tested or simply different components to the 64-bit versions that the Movie plugin uses.)