Created attachment 45390 [details]
Test.html

I only wanted to reformat it...

I'd say it duplicate of issue 105132

Opening the file as .txt just works fine - also when I reformated the file (attechment: test_reformat.html, I had to do
that with Notepad++ since even Eclipse couldn't handle the file) it would take just a little while to open, but then I
am able to scroll without a problem.

Created attachment 45416 [details]
test_reformat.html (Reformatted verision of test.html)

I do think this is not duplicate of issue #105132 - the issue is about java reformat implementatin.

I guess nb is not able to handle reallly loooooong lines. Maybe the profiler can help here.

Wow!, there is so many problems trying to even think about editing of such nice file that I do not know where to start
first :-).

OTOH the file is really huge and IMHO not so typical to be manually edited.

I need more time to evaluate what are the biggest bottlenecks of the editor here. From just brief evaluation I realized
that ages are spend in:
1) rendering of the file - mostly Schlieman's HL
2) parsing of the file by HTML parser and by Schlieman
3) processing of the resulting parse data to AST
4) code folding
5) creation of embeddings based on parser results
...

I cannot promise we can fix them all, but I'll try to find and address more specific problems. I do not expect we will
fix it into beta1. 

Thanks for the report.

After Vita's fix of issue #114016 the impression of the file editing is much better. Now I can scroll like I want
without a high cpu load.

On of the bottlenecks now seems to be the dynamic embeddings creation and subsequent document repainting which take very
very long time, I'll debug it more deeply soon.

I too find editing HTML files (especially on Windows Vista) very slow.
Seems better than M10 though.

The performance is much better than in the beginning => lowering priority to P3.

I opened a reasonably big HTML page (the same I used earlier), 
the performance is much better now.

already fixed