main_image_url method does not return a working link for .tif files

[henrywoody]

There might also be more file extensions that do not work, which, presumably, at least include any image file types that cannot be displayed in the browser.

For sure the method works with .jpg, .png, and .svg.

A potential "solution":

if page['thumbnail'] and page['thumbnail']['source'] =~ /\.tif\.jpg/i
    page['thumbnail']['source'].sub(/lossy-page1-\d+px/, 'lossy-page1-800px')
elsif page['thumbnail']
    page['thumbnail']['source'].sub(/\/thumb/, '').sub(/\/[^\/]*$/, '')
end

However this would always be the link to the image at 800px, which might not always work...