Even if you disagree with the reason might as well give the devs’ stance on it.
> it [single clicking not selecting all] was a special behavior only implemented for Linux, it was not consistent with Firefox on other OSes, and with other browsers on Linux itself. The prefs were causing broken edge cases complicate to handle, taking into account all the possible pref combinations (for example under certain combinations it was not possible to select a word), and having to execute more tests for them. Not removing the prefs would have not saved many resources, since we still need to maintain them.
Why can’t you just have both options?
> Most of the tests should then be able to run with both setups, everytime we touch something around that we'll have to check not breaking it, and so on. Yes, even the simplest pref skipping a line has a cost, and that's why they must be weighted with a benefit.
> Apart from what I already said regarding the will to unify the behavior for the more commonly found case of users moving across OS and browsers, and the cost of options in general, I'd like to explain a further reason why it's not just matter of reintroducing a pref; the change we made here will allows us to experiment more broadly with the unfocused Address Bar contents, for both UX and security reasons.
Keeping browser.urlbar.clickSelectsAll around would make experiments a lot more problematic, and at a certain point we may have to remove the pref regardless, because it would block landing improvements. So we'd end up causing you frustration twice.
We totally understand your point of view on this matter, unfortunately sometimes changes must happen, to be able to evolve things.