Dev - you should open bookmarks UNLOADED. This takes no time or resources. And edited bookmark names are shown as the tab titles, not overwritten and can be reapplied to the tab title while loading if necessary. (By Tab ReTitle.)
Then user can choose which to open and when.

Works well. To make it better have it open the tabs without loading the content or maybe stop loading or unload the tab after loading the page title, then when the user clicks on the tab, load the tab. This will reduce cpu and memory load.

One way to achieve the above is to use Open Bookmarks Slowly together with the "Auto Tab Discard" extension. In Auto Tab Discard options, enable "Discard all newly opened inactive tabs after they get loaded". This will unload the newly opened tabs from memory, and prevent the computer slowing down due to RAM being used up by many open tabs. When you click on the "discraded" tabs (really unloaded), they then load.

Does exactly what it says on the tin. There is even a nice progress page that shows you which bookmarks are yet to be loaded.

A cancel button would be nice, but most of the time closing your browser window works just as well.