[Intermittent] Pages accessed from an unfocused split "New tab" page do not render at all on the latest Nightly

[Softvision-CristinaBadescu]

[Affected versions]:

• Nightly 60.0a1
• Tab Split 0.1.7

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have a clean Firefox profile with the latest Tab Split v0.1.7 installed.
• Have 1 tab open.

[Steps to reproduce]:

1. Open Firefox browser with the profile from prerequisites.
2. Click the "Tab Split" button and click the first tab.
3. Click a hyperlinked element from the unfocused tab and observe the behavior.

[Expected result]:

• The page is loaded and displayed.

[Actual result]:

• The page is loaded, but it is not rendered.

[Regression]:

• I've managed to find a regression window using the Mozregression tool. Here are the results: Last good revision: 6d8f470b2579e7570f14e3db557264dc075dd654 First bad revision: 4403805b3b66f4a130f21d0d2ae036b8fc9d6f5b Pushlog: https://goo.gl/cXRWtb

From the pushlog it seems that bug #1437738 has caused this issue.

[Notes]:

• The blank page will display its content if you resize the browser.
• Here is a screen recording with this issue:

[Softvision-CristinaBadescu]

This issue is no longer reproducible using the steps from the original post, but I've managed to reproduce intermittently this issue using Tab Split v0.1.8 on Windows 10 x64 and Mac 10.12.6, on latest Nightly build 60.0a1 (2018-02-19) by following the below steps:

1. Have 3 websites open in different tabs.
2. Focus the middle tab and click "Tab Split" button.
3. Create a new tab and navigate to a website.
4. Focus the 1st tab from the split.
5. Select a website from the 2nd tab.

Here is a screen recording with the issue: