Can report this as well. Currently on Zen Browser, but I was able to reproduce it yesterday on the most recent version of FF stable branch aswell: Gridlines on Googlesheets are displayed/rendered thicker for some reason. The thickness is correct on first loading the document, but after it finishes loading the rendering updates and lines becomer thicker. Visual artifact does not happen on other chromium browsers: Edge, Vivaldi, Brave. On the left side of the image, you can see a screenshot when the document is loading (correct thickness), and on the right side, the gridlines after the document has finished loading.
