''jscher2000 [[#answer-1067381|said]]'' <blockquote> According to some bug reports, sometimes Firefox 56-59 stops being able to update the recovery.jsonlz4 file due to a problem with a background process (a promise worker process). Firefox 58 (due out next week) will contain some fixes for this that hopefully will solve the problem for most people. If anyone experiences the issue after that, it would be helpful to check [https://developer.mozilla.org/docs/Tools/Browser_Console the Browser Console] for errors messages along these lines: '''Could not write session state file''' Object { operation: "move", path: "C:\Users\user\AppData\Roaming\Mozilla\Firefox\Profiles\1a2b3c4d.default\sessionstore-backups\recovery.jsonlz4", winLastError: 5, stack: "", fileName: "(unknown module)", lineNumber: undefined } SessionFile.jsm:396 That could indicate another variation on the problem that Firefox needs to detect and correct for. </blockquote> Thanks for this information. Funny because after I mentioned that the problem was still occurring after changing style rules, it somehow disappeared by the next day and has been loading correctly ever since. Good to know that the underlying issue will be fixed next release though.