Firefox Community Forum

I'm reposting a question already opened here because a moderator suggested to do so. Actually I though I was posting to the international forum from the URL...

I was trying to access a local HTTPS website of an embedded device (a Siemens S7-1500 PLC) that is using a self-signed certificate, but was unable to go on (attached image #1, in Italian language) due to the the SEC_ERROR_REUSED_ISSUER_AND_SERIAL error. I've browsed a similar PLC webserver in the past, so the fact that the device exposes a similar certificate serial number is not so strange for me, considering also it's self-signed.

The problem is that I cannot follow the instructions of the Mozilla knowledgebase here because I'm not able to identify the correct certificate of the website!

In the attached image #2 you can see that the connection is detected as not encrypted, I suppose because only the form part of the HTML that is posting the data using HTTPS while the rest is using HTTP, but I'm not sure. If I click on the padlock icon (attached image #3) the info about the current certificate is not displayed.

Then I went into Tools > Options and searched for "certificates"; as you can see in the attached images #4 and #5, neither in the Servers tab nor in the Authorities tab I can find any item that is related to 192.168.10.2 (the webserver IP address) or Siemens (the embedded device manufacturer). But unfortunately the error persist! Initially there was a 192.168.10.2:443 line in the Servers tab and I removed it and restarted Firefox, but it didn't solve, so at the moment the situation is the one depicted by the attachments.

I had to use Microsoft Edge to access the website, but I would like to solve this issue and use Firefox instead. Is there anything else I can do to bypass the error? Why doesn't the error page provide a way to correctly identify the wrong certificate using its fingerprint and/or name? Or, maybe, is there a way to disable this check for local IP addresses or for items in a whitelist?

Thanks for your help.

I encountered an issue where pasting multiple images causes the upload to fail. It seems like it cannot handle more than 2 pictures at once. Could you please help me fix this?

It's very tricky the clone a FF profile, so I want to avoid that. (If there is a SIMPLE way to clone a FF profile, that would suffice. I have found no such animal.)

I would like to start Firefox by invoking different UserChrome.CSS files.

Is that possible?

I am not intereted in RUNNING both these simultaneously.

yes, I realize I could go through renaming and unrenaming files before starting FF to achieve this. But, I am I'm looking for a method using native FF resources.

I was trying to reset my password and was having difficulty and finally I was able to change. I also have been trying to delete VPN and have been unable to find how to accomplish it.

There is much more to the following that I received from ChatGPT: The first place to seek answers is obviously with VeePN. I asked ChatGPT the following questions, and as a result, I also have some questions for Firefox. Where can I get answers? I do not like the Edge browser for several reasons. Firefox, as far as I am concerned, is the best browser for my use. Due to the fact I reside in Kaliningrad I must use a VPN to access sites I used to take for granted when I lived in the Czech Republic. This morning, as usual, I tried getting connected to VeePN in my Firefox browser. As usual, it does one of the following: 1) “Something went wrong at our end.” & “try to update” or “contact us for assistance.” 2) Continuously refuses to connect, leaving with the message: “Connection Error. Can’t fetch server config.” 3) Connects very soon after opening Firefox, perhaps 5% of the time I try connecting to VeePN. This morning, I spent many attempts over the course of 2+ hours, and no connection. Sometimes I had to refresh the VeePN extension due to the immediate, continuous, fast popups of “Connection Error. Can’t fetch server config.” Then suddenly, without rhyme or reason, VeePN connected. Also, this morning I decided to test using VeePN on my Edge browser, and it immediately connected, with no hesitation. This begs the question. Is there something about Firefox that may be causing the issue? I have not changed any settings anywhere regarding WiFi or Network & Internet Settings. In addition, sometimes, when I tire of trying to get VeePN to connect in Firefox after decades of connection attempts, I will use my Browsec VPN. I have learned not to use two VPNs simultaneously, one or the other, not both. Also, it is worth mentioning that VeePN is far superior to Browsec, but that is my opinion based on how they both perform after being connected for a good period of time. I can be connected via VeePN all day and have no issues. Browsec requires regular refreshing. Either VPN, however, is affected by the internet connection and the wireless connection between my router and the dongle that sits on my desktop near my PC. Yes — based on what you described, this strongly suggests the problem is more related to Firefox itself (or the Firefox extension environment) than to your internet connection or VeePN service overall. I have added an image of all the Firefox Extensions I use, obviously, some in the list are turned off. I would like to add the information that ChatGPT provided, it is in a Word doc that can be uploaded to help if needed.

I would like to understand how DNS over HTTPS impacts browsing speed and privacy in Firefox.

Details: Hello everyone,

I am currently exploring Firefox privacy and network settings, especially DNS over HTTPS (DoH). I noticed that enabling this feature slightly changes website loading behavior on some networks.

I would like to ask:

Does DNS over HTTPS introduce additional latency? Are there performance differences between providers? Can corporate or public Wi-Fi networks interfere with DoH requests? Is there a recommended configuration for balancing privacy and performance?

I’m interested in both technical explanations and real-world experiences from Firefox users.

Thank you.