What I resent is -- to give two real-world examples -- Chase refusing to let me log in to my account because my browser version is "out of date" (because, as I said previously, I am using the last version of Firefox that is supported under Win 7) or Citi warning me about my browser every time I log on there ... which I take as a "warning" that they are about to "enhance" security soon as well.
I once recommended configuring your Firefox installation to send a custom, modern User-Agent string to your banks' web sites, saying this often worked to get around many institutions' picky browser requirements. Only after you reported no success did I later discover that Firefox had unkindly
removed that feature, stranding everyone in its user base who was dependent on per-site User-Agent switching.
If it interests you, after more Googling, I eventually found
this short thread at Wilders Security, where that unkindness was being discussed. In it, someone finds and posts a link to a Firefox addon bringing back the ability to send custom User-Agent strings to specific sites. So if you want to give that old trick a second try, the addon link you need, and examples of how to configure it, are in that thread. And the currently-latest Firefox User-Agent string can of course still be found
here.
Mind you that while this should finally make sending site-specific alternative User-Agent strings possible for you, there's still the chance that your banks examine more than just User-Agent strings to detect their visitors' browser versions. Again, most don't check more than that, but some particularly paranoid ones can also use browser fingerprinting, SSL fingerprinting, and other JavaScript tricks to determine client versions. In that case, you might investigate these open source projects where people are retromodding modern (i.e. the latest, or near-latest) versions of Chromium and Firefox so they once again run under XP, Vista, and 7:
Supermium (Ungoogled Chromium) for Windows XP and above (direct links:
here,
here):
https://www.youtube.com/watch?v=wsSMmdwh89Y
https://www.youtube.com/watch?v=8VPJ-FCvGd0
Chromium for Windows 7 (direct link:
here)
https://www.youtube.com/watch?v=Aukoov3ioqM
I also found out about this one today, but have not personally tested it yet:
r3dfox (modern Firefox) for Windows Vista and up:
https://github.com/Eclipse-Community/r3dfox
https://sourceforge.net/projects/r3dfox/
Supermium is extra-nifty because its compatibility extends clear back to XP. It also offers an "ungoogled" mode that lets you run it with lots of Google's cruft disabled.
Your only dilemma in using any of these would be whether you would trust them with banking sites -- the irony. They are all open source, and
should be completely benign. But I have not read their source code for you, and can't make guarantees. My advice: try the User-Agent addon for your existing Firefox installation first. Otherwise, they can be wonderful to have around for general browsing, in cases where you encounter sites that refuse to work with Firefox's final ESR for Windows 7, or that want Chrome to play nice at all.
For any classic Mac people out there, I found this too:
PowerFox (modern Firefox that even works on a G4 Power Mac from 2001):
https://www.youtube.com/watch?v=DTCYA3Qa8YM