So, this is different than all the other redirecting issues that I've read about so far. The scenario: I am an admin who has an internal, LAN-only webserver. It is serving up half a dozen web servers running on various ports for various reasons. E.g., Ticketing system on port 8080, an Apache-based Wiki on port 80, Nginx-based GitLab on 443 (the only https site!), etc. etc. If I open the wiki and browse around, everything works great. If I open a new tab and go to Gitlab on 443, everything works great. However, as soon as I go back to the wiki and click a link (or just hit refresh), it takes me to the Gitlab error page, because it stuck an 's' on the http://webserver/wiki.php URL, and now Gitlab is trying to serve up an invalid URL at https://webserver/wiki.php. Even though Gitlab is an internal webserver with a self-signed cert, the CA cert has been imported into Firefox so I get the green lock icon. Troubleshooting / What doesn't work: - The intranet page doesn't end in .dev or .foo, so it's not trying to load Google's website at that TLD. - Changing any settings in about:config doesn't help (at least none of the settings that can be found in the first few pages of a Google search). - Deleting my entire Firefox profile doesn't change anything - Running in Private Browsing / Purple screen doesn't change anything (when loading both websites in the same "mode" - see below). - I have checked the wiki webserver for any extraneous .htaccess files with URL redirects. - I have checked the wiki httpd.conf file(s) for any https redirects - There are no addons installed - Currently running version 60.2.2 ESR. I will try to upgrade to 60.4.0 ESR ASAP. This behavior does NOT happen with 52.x ESR. What DOES work, albeit temporarily: If I go into Preferences -> Clear History -> select the 'Site Preferences' setting, then the wiki will load and I can click around. However, the moment I go back to Gitlab and click on a link or refresh, the next URL I click on in the wiki will attempt to load a https version, Gitlab's webservice at port 443 takes over, and I get a 404. Go back to Preferences and delete the site preferences, and the cycle repeats. This behavior also exists in Private Browsing mode with both sites either in two tabs or separate Private Browsing windows. What works "permanently": If I open the wiki in Regular Browsing mode and Gitlab in Private Browsing mode (or vice versa), I can access each website simultaneously in their respective windows. No https redirect occurs. My conclusion: As soon as I go to Gitlab, some Site Preferences setting gets saved that insists on redirecting all URLs at that domain to https. This site setting gets re-added at every web page invocation/reload, as demonstrated by deleting the Site Preferences and watching the behavior start up again on a refresh. Site Preferences are shared among tabs in both Regular Browsing and Private Browsing, but they aren't shared BETWEEN Regular and Private browsing. This is immaterial to the issue at hand, just an interesting observation. This problem started between versions 52 and 60. I don't know how site preferences are saved. This could be a GitLab problem (generating these site preferences), but then why does v52 work fine...