Ever since I downloaded the latest version of Firefox, I've been having display issues with my bookmarks toolbar. Whenever I mouse over the last five or six bookmarks, their icons disappear until I reload the page. I cannot access any of the bookmarks that have been disappearing in this way, but the rest of my 40+ bookmarks are fine.
I have the same issue. Whenever I go to open my bookmarks drop down window, they pop up and promptly become invisible. Sometimes they will come back up for a second as I mouse over them, but they will stay invisible otherwise and it makes it impossible to select a bookmark with any degree of accuracy. This issue carries through to all drop down windows on webpages as well in my experience. I had absolutely no problems with Firefox until I got force-updated to the newest version.
Start Firefox in Troubleshoot Firefox issues using Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).
Don't make any changes on the Safe mode start window.