MV2 extensions should work in Thunderbird without modification. I've made a couple of simple extensions that work like a charm in both Firefox and Thunderbird, but I'm not sure if more complex extensions would have issues. The documentation says thus:

Some information listed on MDN may not apply to Thunderbird and some API methods may not be supported. Each API page should include a compatibility chart and if that includes support for Firefox, it should work in Thunderbird as well.

Some MV3 extensions will not work in Thunderbird. See this page for list of missing functionality.

navigator.clipboard.read()/write() has been enabled (see documentation). A paste context menu will appear for the user to confirm when attempting to read clipboard content that is not originated from a same-origin page.

Very nice. The old execCommand API was annoying.

Isn't it already game over if malware can write into your hostfile? At least on Windows you need some elevated access for it, which means such malware could just read/write the target program's memory directly instead of resorting to clunky MitM.

At the same time, it is also worth noting that the closed form formula is working with irrational numbers which can only be represented approximately in computers, and thus in some rare cases the method may produce incorrect result due to approximation errors.

I'm nitpicking, but golden ratio can actually be represented exactly in computers. This is because the golden ratio is not merely an irrational number, but also an algebraic number. By definition, any real algebraic number can be represented as an integer vector, which contains a polynomial and two rationals that identify a root of the polynomial. Alas, the multiplication of algebraic numbers is quite involved and certainly far slower than the linear algebra approach for Fibonacci numbers.

Yeah, I also found out when I was manually testing our product's logged-out UX at work and the 2nd trial started logged in.