Ensure list of tabs are opened in order from top to bottom in all cases

[rieje]

Description

When given a list of URLs to open, it is desirable to open them in order from first to last, i.e. top to bottom for vertical tabs. This is not the case when the "position new tab" rule is set to either "panel start", "after active tab", or "first child of active tab", in which case the list of tabs get opened in reverse order (i.e. last url passed is opened as a tab at the top) due to the nature of the rule.

Tree Style Tabs supports this feature so I'm thinking it is useful and/or can be used as reference.

[mbnuqw]

Context: #1577