If I couldn't simply copy my entire configuration as I upgrade versions of Linux I'd be making a painful one time change completely to Chrome and Chromium, which I'd really rather avoid.
The bottom line is that Mozilla let Firefox's market share decline so much that the only two reasons people kept using it were it's not Chrome, and the extension ecosystem. Which is reported to have included a superior debugger, which indirectly made sure a lot of sites implicitly supported Firefox because they were developed using it.
Users don't give the slightest damn that keeping the old XPI ecosystem was hard, and had serious security issues. A huge number of extensions that they depended on have become roadkill on the information superhighway, even if some made the transition with significant changes. Making Firefox into an inferior version of Chrome means for most that the only reason to use it is that it's not Chrome.