hi nludvigson, i'm not sure if we are able to help you with third-party hardware products. you'll likely get a better answer if you ask for help in the linksys community forums at https://community.linksys.com. thank you for your understanding!

Try using Edge or IE to access your Router. IMO, for the few times the user really needs to get at the router settings it makes little sense to fix what Mozilla "broke" for users needing to access the 16-bit block of private IPv4 address spaces; IOW, the 192.168.1.# range of IP Addresses for Router access.

A security fix in Firefox quite awhile ago (mid-2013??) made it impossible (or harder) to access the private IPv4 address spaces which typically use old security protocols like TLS or SSL3. It also affects "local" IP addresses like those used on LAN's and with Routers, which IMO Firefox shouldn't have affected - I think the "private IPv4 address spaces" should have been excluded from the "security fixes".

That said, most later versions of the WRT54G Router can receive a "firmware" update - see Open Wrt - to upgrade the firmware with a pre-made "Firmware Flash file" to update it or one the user created himself or edited. IMO, it might be possible to fix that for Firefox, but I wonder if the time spent doing the fix is worth it.

Personally, I am going to try the "firmware Flash" on a new WRT54GL that I picked up last spring when I saw it for < $50 as I was looking for the hardware to build a new PC; to get Wi-Fi which my current Linksys Router doesn't have. But I haven't gotten around to even connecting it yet; easier to just keep plugging into my LAN when I want internet access for my netbook for the few times in a month that I go online with it.