"Tab Split" button does not work at first click on a page that was dragged or moved in a new window

[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 2 tabs open.

[Steps to reproduce]:

1. Open Firefox browser with the profile from prerequisites.
2. Drag one tab in a new window.
3. Click the "Tab Split" button from the toolbar.
4. Observe the behavior.

[Expected result]:

• The tab is split.

[Actual result]:

• Nothing happens.

[Notes]:

• This issue is also reproducible if you select the "Move to New Window" context menu option.
• This issue is not reproducible if you open a new window by using "Ctrl/Cmd + N" keys combination.
• The tab is split only if you press again the "Tab Split" button.
• Here is a screen recording with this issue:

[fzzzy]

I was able to reproduce this in the bootstrap version, so this is a genuine bug and not a regression.

To get the bootstrap version, clone tab split and then use the command git checkout 4b9ffce to get to the last commit which used bootstrap.

[ianb]

Note this this applies to any new window, e.g., if you use Cmd-N to open a new window. Also if you have multiple windows open when you install the extension, only the foreground window will have a working/active button.