Considering that Firefox takes quite a while to launch, could someone recommend an application that I could use instead when it comes to viewing disparate (not interlinked) offline .html files ?

i do not know any but some one else in this forum does
I use Internet 7

Cheers

Internet Explorer, that's what I've always use for just viewing HTML files offline because as you've found out Firefox takes a bit of time to load. Although, once Firefox does load once each subsequent loading is faster.

For Internet Explorer you can make a right-click Send To shortcut to it. If you wish to get more involved you could edit the filetypes and add Internet Explorer to the HTML filetype so that when you right-click an .html file you'd have an "Open In Internet Explorer" shell extension. However the Send To shortcut is the quick and easy way, and requires no messing with the filetypes or registry settings.