cannot sync Firefox ESR 52.9 login passwords with quantum
I still use the Quantum 96 portable along with Firefox ESR 52.9 for certain sites due to the superior customization and functionality of the latter via extensions that do not work on Quantum. However, I would like to sync the ESR passwords with Quantum, but I cannot login into Sync on ESR since "sign in" results in "Blocked by Content Security Policy."
Hello. Try this usual solution, by deleting browser cache or running the browser in safe mode.
On the other hand, because 52.9 ESR is long since unsupported, you can use 'fork' like Serpent by roytam1 or Basilisk browser. If you also want max customizability (UI before Australis 29) you can try Pale Moon.
All of these browser still and will continue to support XUL/Legacy Add Ons, while also providing latest security patch and compatibility fix for modern web. Hope this helps.