On a purely technical level, I think it should be possible to write some sort of "emulation layer" that exposes a Chrome-flavored WebExtension sandbox and translates the calls to the respective Firefox APIs wherever possible.
However once that functionality exists, where would you actually get those extensions from and how would you install them? Firefox famously doesn't allow extensions to be installed that are not registered with the Mozilla's store, and Chrome extensions obviously aren't. Even if they relaxed that rule, you'd also expect automatic updating to work, just like for "native" Firefox extensions.
So in effect, Firefox would have to integrate Chrome's store as a second legitimate extension repository. That would be a boon for users, but I can think of reasons while neither Mozilla nor Google would want to do this:
For Mozilla, it would mean loss of control over half of the extension ecosystem: They cannot ban Chrome extensions, they have no control over their approval process etc, but now users could install them and receive continuous updates - sonin effect, Google would suddenly be able to push updates to Firefox installations.
On the other hand, Google would lose its moat around the extension store: Everything that Chrome offers would now be automatically supported by Firefox as well.
So I think, neither would Mozilla want to include Chrome's store in Firefox, nor would Google allow that.