Enabling tab-bar-mode grows the frame's height (not always, just the first
time). Disabling the mode does not shrink it. Is that intended?
Is this on Windows?
(let ((initial (assq 'outer-size (frame-geometry))))
(tab-bar-mode 1)
(tab-bar-mode 0)
(list (assq 'outer-size (frame-geometry)) initial))
=> ((outer-size 689 . 687) (outer-size 689 . 671))
On GNU/Linux it's correct:
=> ((outer-size 678 . 633) (outer-size 678 . 633))
OTOH, for the tool-bar the problem exists:
(let ((initial (assq 'outer-size (frame-geometry))))
(tool-bar-mode 1)
(tool-bar-mode 0)
(list (assq 'outer-size (frame-geometry)) initial))
=> ((outer-size 678 . 587) (outer-size 678 . 633))
in both Emacs 27 and GNU Emacs 25.2 (x86_64-pc-linux-gnu, GTK+ Version 3.22.21)