STR: 1. Open Eyedropper (Colorpicker) and see that text fonts are awful blurry, compared to sharp and clear text fonts in Firefox GUI

I can't reproduce this issue. I have tested on Windows with FF57 and FF56. Can you please provide more details about the computer you tested on? OS, monitor size and resolution could help.

Fortunately, I can't reproduce this issue anymore, on various Firefox versions, so it could be GPU driver issue, as I only updated it from this time, or maybe some other odd and magic thing.

Ups, I'm reopening this issue, as looking on my attached screenshots, looks like I missed 1 major point, as one of Eyedropper is bigger then other. Here proper STR: 1. Open this URL - about:blank 2. Set zoom level to 110% 3. Open Eyedropper (Colorpicker) and see that text fonts are awful blurry, compared to sharp and clear text fonts in Firefox GUI zoom levels: 30% - affected 40% - affected 50% - affected 60% - affected 67% - affected 70% - affected 80% - affected 90% - not affected 100% - not affected 110% - affected 120% - affected 130% - affected 133% - not affected 140% - not affected 150% - not affected 160% - affected 170% - affected 180% - affected 190% - not affected 200% - affected 210% - affected 220% - affected 230% - affected 240% - not affected 250% - not affected 260% - not affected 270% - not affected 280% - not affected 290% - not affected 300% - not affected So maybe Firefox shound't zoom Eyedropper (Colorpicker), as easy fix for this (or at least I think that it will be).

I see what you mean now. Yes the eyedropper zooms and unzooms with the page. This is a problem that is already tracked in bug 1288389, so I will close this bug as a duplicate of 1288389.