I just did rebuilt my computer and have Windows 10 and Firefox 54.0 installed.

When I attempt to open several of my bookmarks at the same time by using the "Open all in tabs" feature I find that the first bookmark loads and displays while the rest of the bookmarks get a "placeholder tab titled "New Tab" that does not load until I click on the tab. At which time the tabs title changes to the bookmarked page and the content loads. I understand that this is done so that opening a large number of tabs all at the same time does not cause issues in Firefox. I found several posts that mention going into About:config and changing the "browser.sessionstore.restore_on_demand" setting. I tried this and restarted Firefox and my computer but this does not fix the issue when opening multiple bookmarks at the same time. I have disabled all of my addons for testing and do not see any changes. Is there a way to force Firefox to load multiple bookmark tabs in the background?