set init width of the perf dialog, to prevent scroll bars when show, The minimum width is still 600px
TB 17 use old alert API
SeaMonkey use GetIdentityForHeader instead of getIdentityForHeader
User can open 2 perf dialog from 2 top window even not instantApply
Fix info window issue for TB17, seems it don't like 'let' in CDATA, use var instead
minor msg change