Looks like multiline/multi-row tabs are broken again in FF 71.
As indicated in the question. At some point (FF 69) I had to turn from Tab Mix Plus to a patch from off the web which worked for several versions. Now that's broken (may have something to do with chrome/userChrome.css loading - but that's just a semi-informed speculation).
I believe I've set it up correctly (correct files in the correct locations) but so far it's not working. It seems the github site doesn't take bugs/questions so I'm trying to remember how to debug these files where the first question in this case would be: am I even loading what I think should be loading? There's a JS loader patch to be put (in my case) under c:\program files\Firefox Developer Edition - and then the files for multirow in one's profile directory chrome subdirectory. Roaming (users/xyz/appdata) as opposed to Local - however did notice that one should clear out one's startupCache directory (under Local). Which I did.
Additional System Details
- Shockwave Flash 32.0 r0
- User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:71.0) Gecko/20100101 Firefox/71.0
Tab Mix Plus hasn't been available since Firefox 57 Quantum was released on Nov 14, 2017. userChrome.css mods have been needed since then to get that functionality.
Looks like Fx71 received some fixes om Oct 11 multirow functions.
In Firefox 69 and later you need to set this pref to true on the about:config page to enable userChrome.css and userContent.css in the chrome folder.
- toolkit.legacyUserProfileCustomizations.stylesheets = true
Additionally, I wonder whey you are screwing with the Nightly development version when you don't have clear knowledge of how userChrome.css works to modify Firefox. And you also don't understand the difference between Nightly and Web Developer / Beta (which is now Fx 70); my reasoning for saying that is that the Nightly builds are where changes such as that first appear and those changes sometimes happen more frequently as the changes are being tested. Sometimes the changes are inadvertently broken and need to be fixed with a later version; part of the testing process. Plus Nightly gets so many more updates over its 6 week run (like every night) than the Developer / Beta version receives which get a 2 or more revisions per week over its 6 week run up to Release.
Many years ago (before Firefox 4.0 came out) the "Nightly" version was labeled Minefield and used a blue logo image that had a "burning wick", like a "bomb" would have. IMO, that was developer humor to indicate that it could be vary unstable at times and users should be aware that it could "go off" at any time.
I wonder why the hell any sane person would use such a version for "normal use"; possibly needing to modify their userChrome.css file repeatedly over the course of testing a newly installed or updated version over the course of 6 weeks.
Plus, the real bad news is that IMO userChrome.css may be well on its way to being totally gone from Firefox. I base that SWAG on a new preference that was added for Firefox 69 - toolkit.legacyUserProfileCustomizations.stylesheets - which requires the user to toggle that pref to True so that userChrome.css will actually do anything in a new Profile. And that is another change that was made in Firefox 67, where a new Profile is automatically created when the user installs a 2nd version [or subsequent] of Firefox.
See this for more information: https://www.ghacks.net/2019/05/24/firefox-69-userchrome-css-and-usercontent-css-disabled-by-default/