Do security settings for the user profile allow for the running of portable executables? If so, one kludgy way to work around this would be to download and use an older Firefox ESR build (say one earmarked for continued Windows 7 support through March 2025, like ESR 115, current PA build is v.115.14.0 -
scheduled to get updates through v.115.21 on 04 March 2025)
specifically from Portable Apps (
not the official installer build), where the various about:config settings from the instructions provided from the various links to ensure HTTP support mode should still work. Then, if it works and when ESR 115 stops getting security updates or you don't bother getting them, just treat it like Internet Explorer. It won't update, it'll just sit there unupgraded, forever Firefox ESR 115, so long as you don't install and use the Portable Apps Launcher to update it. You technically don't even need Portable Apps to install it. Just unpack and launch, and dump a shortcut into the appropriate folder for the start menu.
In theory, you should be able to even run regular installed Firefox and portable Firefox ESR in parallel so long as each app uses their own dedicated profile settings, however I can't personally test and confirm this as I no longer run Windows at home again, and the last time I tried doing this, Mozilla hadn't fixed the issue yet, and the two would butt heads and refuse to run if the other was launched.
Of course, the other workaround to conflicting parallel Firefox launching would basically shove all regular and basic internet access off to Edge/Chrome/Vivaldi, and treat the portable Firefox ESR 115 build like the weird, modern bizarro equivalent of IE for Windows 10/11... dedicated to only this one job. Which kinda makes sense, 'cause you're gutting a lot of security measures from running in the browser. You could even theoretically firewall the app down to only be usable for this purpose.
https://portableapps.com/apps/internet/firefox-portable-esrhttps://sourceforge.net/projects/portableapps/files/Mozilla%20Firefox%2C%20Portable%20Ed./But seriously,
follow these instruction and also change all of the following
about:config settings before even attempting to connect and
follow these last instructions, and
make sure the location is not in the history before you even start.
browser.urlbar.autoFill false
browser.fixup.fallback-to-https false
browser.fixup.alternate.protocol http
network.stricttransportsecurity.preloadlist false
Hope this helps!
Edited to correct links, I accidentally linked the source code instead of the compiled binaries, and edited for further clarity. Oops, sorry!Last edit, I promise. Sorry, my brain's not as sharp as it once was, and I keep remembering stuff that I should have included to begin with.Anyway, you could also in theory install
via the official Firefox ESR installer and attempt to disable auto-updates (though it's worth noting that disabling auto updates means some idiot could also accidentally re-enable auto-updates hosing you again after April 2025), but I specifically recommended going with the Portable Apps Firefox ESR build because that guarantees that the update mechanism is thoroughly and completely hosed and broken, forever* preserving the build installed.
*forever, or until the next catastrophic hardware failure, whichever comes first