Router firmware is usually designed for Internet Explorer because it is the most basic. There are many cases where router firmware will not load in Firefox (for example TP-Link routers).

Please contact your router manufacturer for more information.

That's all well and good, but it worked before the *firefox* update. There hasn't been any change to the router in ages. Linksys will say, correctly, that they haven't changed anything, and if it doesn't work on firefox, just use another browser. Is mozilla's response to use another browser because their update can't perform the task?

I am simply speaking from personal experience. Usually the router firmware is designed to run on Internet Explorer because it is the most basic web browser and it updates the least.

I've been looking over the release notes and the changes that were made in the recent version. Depending on what version you updated from, it don't see any changes that would cause your router firmware to stop working.

Can you please try running Firefox in Safe Mode to see if you are able to access your router? Safe Mode is a diagnostic mode that will temporarily disable your add-ons, disable hardware acceleration and revert some settings. This will help us to rule out any issues with setting or add-on conflicts, since Safe Mode is similar to running Firefox with the factory settings.

No difference in safe mode. It still loops back asking for the password until you click cancel, then 401's.

Do you have the "Do Not Track" feature turned on? It's turned off by default. See How do I turn on the Do Not Track feature?.

This is an old thread but the reported solution was to UNCHECK (turn off) the "Do Not Track" setting in your Firefox Privacy options http://community.linksys.com/t5/Wireless-Routers/Firefox-cannot-access-WRT120N-setup-but-IE-can/td-p/366977/page/3

In Firefox 49, go to your Privacy Options, click manage your Do Not Track settings and uncheck "Always apply Do Not Track".

P.S. http://kb.mozillazine.org/Error_loading_websites#Accessing_a_router also says, Some routers cannot be accessed if the do-not-track option is selected.

Nnnnope. Disabled. I even tried enabling and then disabling again. Also deleted cookies/history. Still 401'd

If no one has any other suggestions:

• Try the basic troubleshooting steps in the Troubleshoot and diagnose Firefox problems article
• Post a question on http://community.linksys.com
• Just use Internet Explorer or Chrome to access your Linksys router, which was the "solution" chosen earlier this year in the thread, https://support.mozilla.org/questions/1109146 Firefox won't let me connect to change my router settings

A couple of thoughts

• Someone more knowledgeable than me may be able to get clues from the Network console results
• It could be worth trying to spoof either an earlier Firefox version or a different browser by using an add-on such as
  • UAcontrol addons.mozilla.org/firefox/addon/uacontrol

There would be a workaround of using Firefox Portable ESR as an additional browser, but that does not seem worth the effort as alternative browsers already have access. Unless for some reason you access the routers features on a regular basis.

atropos92 If you do post in Lynksys community support we may get an official answer and a reason for this problem, or at least confirmation others have the problem. You mention the firmware is updated I wonder if there could be a problem in the latest firmware. If you do decide to post in the support forum perhaps you will let us have the link for your thread.

• Support site is I believe http://community.linksys.com/?category.id=English