It's not clear whether they actually know something or just want to avoid solving the problem...

Couple questions:

• Did this just start today with Firefox 29, or was it happening with your previous version of Firefox?

• Does your bank require supplemental software such as Trusteer Rapport or an add-on in order to use their site?

Another thought: Many users have recently become more aware of privacy and either made changes to their cookie settings or installed extensions that stop some information from reaching websites. While this reduces tracking, it also can cause some site functions to break.

As a test, try using the bank site (1) in Firefox's Safe Mode (2) in a Private Browsing window. This will help bypass restrictive cookie settings, as well as other filtering behaviors of extensions, to see whether those are a factor.

You can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled

In the small dialog that should appear, click "Start in Safe Mode" (not Reset)

Then open a private browsing window using either:

• Ctrl+Shift+p
• 3-bar menu Firefox button > New Private Window
• File menu > New Private Window

In that window, can you get into your bank?