I've just transferred from one Windows 10 install to another, and wanted to transfer my Firefox profiles along with me. Initially when I transferred over my main profile, the addons worked at first but broke after a short while (specifically there were still as many addon buttons in my toolbar as before, but they were all blank and did nothing), and wouldn't restore after shutting down and reopening Firefox. At first I tried disabling and reenabling each extension, and that worked, but after shutting down and reopning Firefox, they were all broken again. I looked for fixes and tried the solutions in this ask: https://support.mozilla.org/en-US/questions/1260445; first, I tried jscher2000's solution of "deleting" extensions.json by renaming it, but it only fixed a couple addons (BitWarden and uBlock Origin, mainly). Then I tried cor-el's solution of deleting combatibility.ini, and that still only had BitWarden, uBlock Origin, and maybe one or two others working - it also seemed to slightly further the problem, as the toolbar was now set to default without even the blank addon buttons, and the extensions overflow button now just opened about:addons. But, then I deleted the profile and copied it over again, but this time I preemptively went into extensions.json and changed all the paths to the new correct path (I also did so for the one path address in pkcs11.txt just in case, because it was the only other thing that came up in a search in the profile folder that had that hard-baked full path that might need updating; I don't know what pkcs11.txt does but I just wanted to be sure), and then (not sure if this part matters quite as much) did Create a New Profile and selected that existing copied-over folder as the folder for that profile to use. Lo and behold, all my addons worked! And they've continued to work as normal and not break through several times of closing and reopening both that specific profile and Firefox overall, and even with a couple shut downs and restarts of Windows. However..... I tried doing that exact procedure (copying over profile folder, editing the paths in extensions.json and pkcs11.txt to be the new correct ones, Create a New Profile and selecting that folder) for my secondary profile, and yet still most addons end up nonfunctional with a defaulted toolbar and extension overflow button opening about:addons just like in the main profile after I did the compatibility.ini fix (even though I didn't even touch it on this profile). After several tries of doing that with differences in naming of the new profile, or also trying to delete compatibility.ini, still I got the same result. Then I tried doing the "disable and then reenable each extension" thing again like I tried first on my primary profile, and it brought the extensions back and in their correct order in the toolbar, but when I exited Firefox and reopened it, they were back to the multitude of blank buttons (which, at least, was a change from before). I have no idea what's different, as far as I'm aware I'm doing the exact same thing that worked on the first profile yet it's still ending up broken. I've also now tried copying over a third profile in the same manner, and it works perfectly just like the first/primary profile did. But the second profile still just will not work.