Can't open links from zathura: Failed to execute default Web Browser, but default web browser is set and working from other pdf viewers

When I try to open any pdf link using zathura (all that I have tried so far), I get the following:

Failed to execute default Web Browser
Input/output error

When opening Default Applications, firefox is already selected under Web Browser. All other pdf viewers on my system can open the links as expected.

How can I fix this to make opening pdf links using zathura available again?

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