Is this with a website?

Load the web page. Then, to reload the page bypassing the cache and force a fresh retrieval; Ctrl+Shift+R (Mac=Command+Shift+R)

Try this several times.

Remove History For One Site {web link}

Open the History Manager <Control> (Mac=<Command>) <Shift> H. In the search bar, enter the name of the site. Right-click on one of the listings and select Forget About This Site. This should remove all information, including any site settings

Firefox shows a purple shield instead of a gray shield at the left end of the location/address bar in case Enhanced Tracking Protection is blocking content. You can click shield icon for more detail and possibly disable the protection. You can check the Web Console for messages about blocked content.

• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

when trying to access my outlook account after successful authentication I get a "failed to load javascript" error. Prior to last browser update (last time I checked mail on pc) everything was working fine. Firefox 79.0 64bit Windows7 home premium sp1. here the complete message: cId: 7810C50E8ED44602A6386E7A8AAD79A3 app: Mail st: undefined reqid: undefined wsver: undefined efe: undefined ebe: undefined et: ClientError esrc: Script err: Error: Failed to load javascript. estack: 39/_</t.prototype.onLoadFailed/</<@https://outlook.live.com/mail/0/?bO=1&sessionId=ec7c7ede-b5d1-490a-be29-837f0b75644a:351:57463 u/</<@https://outlook.live.com/mail/0/?bO=1&sessionId=ec7c7ede-b5d1-490a-be29-837f0b75644a:344:2574 u/<@https://outlook.live.com/mail/0/?bO=1&sessionId=ec7c7ede-b5d1-490a-be29-837f0b75644a:344:2679 l/<@https://outlook.live.com/mail/0/?bO=1&sessionId=ec7c7ede-b5d1-490a-be29-837f0b75644a:344:1616 l@https://outlook.live.com/mail/0/?bO=1&sessionId=ec7c7ede-b5d1-490a-be29-837f0b75644a:344:1361 39/_</t.prototype.onLoadFailed@https://outlook.live.com/mail/0/?bO=1&sessionId=ec7c7ede-b5d1-490a-be29-837f0b75644a:351:57059 39/_</t.prototype.import/this.promise</</</<@https://outlook.live.com/mail/0/?bO=1&sessionId=ec7c7ede-b5d1-490a-be29-837f0b75644a:351:56081 u/</<@https://outlook.live.com/mail/0/?bO=1&sessionId=ec7c7ede-b5d1-490a-be29-837f0b75644a:344:2574 u/<@https://outlook.live.com/mail/0/?bO=1&sessionId=ec7c7ede-b5d1-490a-be29-837f0b75644a:344:2679 u@https://outlook.live.com/mail/0/?bO= ts: 2020-08-23 10:53:08Z </blockquote>

Disabling "Privacy Pass" and "Redmorph Browser Controler" extensions solved the issue. Thanks for helping