1451401 - Opening a new tab and then causing a Switch To tab from the AwesomeBar always results in a short spinner

Status: NEW

(Firefox :: Tabbed Browser, defect, P3)

Description

[Mike Conley (:mconley) (:⚙️)]

STR:

0) In a recent Nightly, install Spin Doctor: https://mikeconley.github.io/spindoctor/
1) Open mozilla.org in a tab
2) Open a new tab
3) Type "% mozilla.org" in the URL bar so that the previous tab will be switched to when you press enter
4) Press Enter

ER:

No Spin Doctor beep.

AR:

Spin Doctor beep. Quite reliable too.

Interestingly, I seem to need to open a new tab in order to hit this. Using Switch To Tab from the URL bar from any other kind of tab doesn't seem to cause this as reliably.

Comment 1

[Mike Conley (:mconley) (:⚙️)]

I think I know what's going on here. Anytime we use Switch To Tab from the about:newtab page (or any page we consider "blank"), we'll switch to the new tab after closing the about: page.

That means that we don't keep the layers around to display to the user and so we fall back to showing the spinner during the tab switch.

Here's where we do that switch and removal:

https://searchfox.org/mozilla-central/rev/a0665934fa05158a5a943d4c8b277465910c029c/browser/base/content/urlbarBindings.xml#754-757

So in a way, this is a variation on bug 1425887, because the underlying cause is the same: we are switching to a tab, having just removed the previous tab, and so we don't have the old layers around anymore to keep showing.

We do a similar thing when exiting customize mode it seems.