Weird. Does version 3.3 install normally?

https://addons.mozilla.org/en-US/firefox/addon/empty-cache-button/versions/

EDIT:
Oh, now I see. To be honest I have no idea why AMO put version 48.0 as a limit version. It's supposed to be 53.0+.

Thanks for bringing the ESR version to my attention, will find out more and make a decision.