Turning letterboxing off results in newtab not rendering

STR (using latest alpha)

• TB not connected
• flip LB off
• in a new tab load a file:// scheme
• nothing shows
• toggle LB on, change to test tab, it shows
• now you can use that tab regardless of the LB pref, but new tabs will exhibit the issue

Related to newtab window "clamping" I think - I'll let you debug it = @ma1

behold my mighty gif making skills