Then page loading takes unreasonably long time. Like 30-60 second or more. And thumbnails are really smaal, about 4k each - so theres not really much data or network traffic.
With 50 pics all is fine (loading time around a second); 90 pics also (loading time about a second); after 100 or so pictures on page you can see how FF struggles, first it displays some 20 images, then it 'thinks' then few more images, then it 'thinks' then few more images.. and so on.
Processor does not seem to get much load at that time.
When reloading the page with cached images, FF renders quickly - when forcing a shift reload, then it struggles again.
This is not a server problem as when tried with different browsers the problem does not occur on first page load or forced reload without cache. Only with FF this happens.
Also, when thumbnails are replaced with just text about image name as links the rendering is instant.
Tried safe mode with no addons - problem still accurs.
System has Phenom II X6 1055T processor with 8gigs of ram.
FF cache has been placed on ramdrive for speed.