(This is a followup to bug 1563208 -- likely an unrelated issue to that bug, but the same site)

STR:

1. Load http://www.ntv.com.tr/ in Firefox Preview Nightly on Android
2. Watch the pageload throbber.
3. Do the same thing in Chrome on Android.

OBSERVATIONS:

• In Firefox on Android, the pageload throbber doesn't complete until the page is visually complete (when pieces have stopped appearing).
• In Chrome on Android, the pageload throbber disappears really early, well before the page is visually complete (for me, only the top-bar is visible, when the throbber disappears in Chrome, and the rest of the page loads over the next several seconds).

This leads to a perception that Chrome is loading the page faster than we are. We should investigate what's going on here and what's responsible for the difference in pageload throbber behavior.

One other interesting data-point: if I use Firefox-on-Desktop/Chrome-on-Desktop's devtools responsive-design-mode (with a Samsung Galaxy device as the chosen phone to mimic), I consistently see the tab-loading-throbber keep animating until the page is visually complete. It's only in Chrome-on-Android where the load-bar seems to complete really prematurely. So Chrome-on-Android may be getting up to some shenanigans [though even so, perhaps there are good reasons behind the hypothetical shenanigans; so still probably worth investigating & understanding what's going on, as if this were a Firefox bug.]

Interestingly: in Chrome-on-Android, after the load bar has disappeared, try pressing the browser's kebab menu (the three-dots at top right). This menu still shows a "stop" ("x") button instead of a reload button for several seconds after the pageload-bar disappears -- it still renders as an "x" for the rest of the (apparent) pageload time. Eventually it changes to a reload icon (and it changes dynamically, if you leave the menu open and watch that icon).

In contrast: in Firefox Preview on Android, the equivalent icon seems to be exactly coupled to the pageload-bar (which makes sense).

So: from the perspective of this stop/reload icon, we seem to agree with Chrome on pageload progress/completion. It's just that Chrome has some other decoupled metric/event that it's measuring & reporting via for its pageload throbber-bar.

Here's a profile of the pageload in Firefox Preview Nightly (on Android), in case it's helpful in analyzing what might be going on:
https://share.firefox.dev/37xRXTA

...and here's a screencast showing how this pageload looks in Chrome-on-Android. Pay special attention to:
(1) the blue pageload-throbber-bar (below the URL bar) -- this disappears at around 0:08 (just after the cookie disclaimer appears at the bottom).

(2) the [X edge] advertisement/logo that appears & animates up from the bottom of the screen at around 0:16-0:17 (as far as I can tell, this is the last visual piece of the page to finish loading/rendering, aside from the continually-changing slideshow)

(3) the "x" stop-button in the browser menu at the top right -- this changes to a "reload" icon at 0:20, which I think is what corresponds to the page really finishing loading (and this is the time where Firefox would make the same button-icon-change and finally hide the pageload-throbber)