Main question: my ISP compresses HTML and images, unless I press Ctrl + Shift + R on Chrome (and Firefox). So, how does the ISP know that I forced a refresh?
I recently switched to Vodafone 4G router, from my good unnamed broadband. I realized that images looked blurry, and many websites looked strange. But when I connected back to broadband, things were back to normal. Turned out that Vodafone actually compresses data (very lossy compression!!). It made jpeg images very blurry, and removed whitespace from the HTML. It even removed the comments that I wrote inside HTML on my website. The URLs in the HTML are not changed; the blurry images appear to be hosted at same URL. The same effect when hitting Ctrl + R, or when clearing my browser's cache and just loading the page.
All this was expected, except, when I force reload using Ctrl + Shift + R, the uncompressed web page appears! This means that my own webpage's code had those comments and whitespace intact. If I press Ctrl + R after this, it showed the compressed version again. I tested this multiple times on Chrome and Firefox, and on 2 laptops.
Here is my question: how does Vodafone know that I pressed force reload?