Yonke imikhiqizo Isithangami Sokwesekwa

Hello, I am currently having an annoying issue when browsing Firefox on particular websites. There's this large, irremovable white bar at the bottom of the screen that appears when I'm browsing particular websites (it only appears on those and those websites only), but it never appears on other websites and there doesn't seem to be a way to remove it. I've tried clearing cookies and cache, disabling certain extensions but nothing has seemed to work so far. I'm currently using the Firefox Nightly, but the same exact issue is present on the same exact websites (developer.mozilla.org, codewars.com, etc.) on my regular version of the browser. This is getting really annoying and I don't want to switch to a Chromium-based browser, so is there any way to fix this annoying issue? Any help would be greatly appreciated.

I saw many tutorials on making self-signed certificates get a lock sign of trusted certificate, which were installing the root certificate of authority in firefox which i did, and also installed in windows, i am using latest version of firefox developer edition, this is error i recieve:

Websites prove their identity via certificates. Firefox Developer Edition does not trust this site because it uses a certificate that is not valid for 192.168.0.102. The certificate is only valid for the following names: localhost, 192.168.0.102, 172.20.10.3