When selecting the awesombar, the font size changes underneath the cursor to a larger one. This is:

a) A visually jarring transition.
b) Inconsistent with the display of URL or site titles everywhere else in the app, such as the tabs.
c) Makes some URLs that would previously fit no longer fit.
d) Moves the cursor from underneath the users' mouse(!), as the selection position now jumps to elsewhere in the URLbar due to the enlarged font.
e) Makes the regression from Bug 1585980 worse.
f) Of questionable use, as if the default font size weren't legible enough, then we'd still have this too small font size everywhere else in the application.
g) Inconsistent with the behavior of other applications or how UI elements are expected to behave.

This can be fixed with "browser.urlbar.update1.expandTextOnFocus=false".

I think the most problematic part here is the selection one, that is already tracked in bug 1601339.
So this is mostly about the "visual" effect, while bug 1601339 is about the functional problems.

The "jarring" visual effect is a subjective thing, as well as the inconsistency is a UX choice. UX has been notified about this feedback and is evaluating it.
Fitting/non-fitting urls should not make much difference, the change is mostly about zooming in the input field text on focus, we always zoomed the results view text (even if a little bit less 1.05em vs 1.14em).

If you don't feel strongly about the "jarring" visual effect, I'd suggest to just dupe to bug 1601339 to reduce confusion between the 2 bugs.

I do also find it a bit annoying having the increased font size.
Could it be an option to have a configuration item to set the font size?

There is already, browser.urlbar.update1.expandTextOnFocus

Sorry for the quick feedback without many details.

Basically:
I don't mind at all update1 font changes and other options.

But very important:
There should be an option to avoid the growth/expansion of the address bar like requested here.

Workaround:
The only solution currently is to disable the whole thing. While I'd expect "expandTextOnFocus" to fix that, it really just makes the text stays the same as non-focus but the bar still grows.

Why is it bad:
Covers too much space, unneeded, blocks the tab colors for Temporary Containers/Multi-Account Containers addons. Feels like Firefox is trying to pull a forced mobile design on a desktop input text box just for the heck of it.

(In reply to Marco Bonardo [:mak] from comment #3)

There is already, browser.urlbar.update1.expandTextOnFocus

Oh, thanks! :)
I did not know that one

Downgrading as this feature is now disabled.