Unfortunately, if your credit union decided to stop their customers from using Firefox to access their website, there's not really much that can be done from your end. I can't say I've ever seen a website block Firefox specifically.

What makes you think that you aren't able to login using Firefox?

You can try these steps in case of issues with web pages:

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• hold down the Shift key and left-click the Reload button
• press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• press "Command + Shift + R" (Mac)

Clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Options/Preferences).

"Remove the Cookies" for websites that cause problems:

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Manage Data

"Clear the Cache":

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Clear Data -> Cached Web Content: Clear

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

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History -> Show All History" or "View -> Sidebar -> History").

Using "Forget About This Site" will remove all data stored in Firefox from this domain like history and cookies and passwords and exceptions and cache, so be cautious. If you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of involved files.

If you revisit a 'forgotten' website then data from that website will be saved once again.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

You can also try using a Firefox addon to fool your bank's website into thinking you're using Chrome. If it works, that would prove they are blocking Firefox from their site.

See these addons: https://addons.mozilla.org/en-US/firefox/addon/user-agent-switcher-revived https://addons.mozilla.org/en-US/firefox/addon/uaswitcher/

But you need to be careful as sometimes when websites switch to supporting only one web browser like Google Chrome, this can mean things will break in the other browsers like Firefox. So some things might not work in the bank's site even if you manage to sneak in by pretending to be Chrome via the Firefox addon.

The addon works by changing the useragent which is a ID for the browser. The website reads the useragent to find out what browser you're using. This useragent switching trick almost always works but sometimes can fail. Good luck!

Big thanks to cor-el & Noah, and just before trying your fixes I repeated my login attempt to find it succeeded, as did my months older system copy. I'm convinced the credit union God has rebuked his charge (with 40 yrs PC maintenance & mainframe software I strongly suspected an "in-house" glitch) and am not surprised others have forced CUA to "undo" something. Unfortunately I cannot repeat the fault nor test your solutions, and they trimmed out my summary of my own resets & extention removals from my Question 'coz I added them as a ps footnote after adding my personal details :( . Thanks heaps guys; well done anyway. Now to mark it Solved (somehow?).