Randomized browser size doesn't take letterboxing into account

[Oregano1963]

Expected behavior

I expected to see no letterboxing when not changing the window size of MB and for it to be large enough to not have to scroll sideways on certain websites.

Actual behavior

I actually see that the randomized window size doesn't take letterboxing into account and so overshoots and makes the window wider than it has to be. Moreover, sometimes the window is too small and certain websites like curseforge won't fit and will include a sideways scroll bar.

Admittedly, I'm not sure whether to count this as a bug report or feature request but what I'd like is for the starting window sizes to match the allowed window sizes and for the minimum window size to be increased. For instance, Librewolf has a moderately larger default window size than MB and I've never had issues with it.

Steps to reproduce

1. Open browser with vertical tabs
2. Search anything
3. Observe Letterboxing on the sides

Issue reproducibility

Always reproducible

When did this start?

15.0

Does it work in latest Firefox ESR?

I don't know

Browser version

15.0

Installation mode

System install (using an installer or a package manager)

Operating system

Unsupported OS (please specify below)

Other OS

NixOS 25.05

Profile testing

I have not tested with a fresh profile

VPN Status

Not using any VPN

Additional Information

Sizes of MB when opening them repeatedly Letterboxing

This issue only happens when i use vertical tabs and it also affects the Tor Browser

[leoheitmannruiz]

It seems this issue is being tracked at https://gitlab.torproject.org/tpo/applications/tor-browser/-/issues/44096