TenFourFox Feature Parity Release "30.2" (SPR 2) is now available for testing (downloads, hashes, release notes). The reason this is another security-only release is because of my work schedule and also I spent a lot of time spinning my wheels on issue 621, which is the highest priority JavaScript concern because it is an outright crash. The hope was that I could recreate one of the Apple discussion pages locally and mess with it and maybe understand what is unsettling the parser, but even though I thought I had all the components, it still won't load or reproduce in a controlled environment. I've spent too much time on it and even if I could do more diagnostic analysis I still don't know if I can do anything better than "not crash" (and in SPR2 is a better "don't crash" fix, just one that doesn't restore any functionality). Still, if you are desperate to see this fixed, see if you can create a completely local Apple discussions page or clump of files that reliably crashes the browser. If you do this, either attach the archive to the Github issue or open a Tenderapp ticket and let's have a look. No promises, but if the community wants this fixed, the community will need to do some work on it.
In the meantime, I want to get back to devising a settings tab to allow the browser to automatically pick appropriate user agents and/or start reader mode by domain so that sites that are expensive or may not work with TenFourFox's older hacked-up Firefox 45 base can automatically select a fallback. Our systems are only getting slower compared to all the crap modern sites are adding, after all. I still need to do some plumbing work on it, so the fully-fledged feature is not likely to be in FPR31, but I do intend to have some more pieces of the plumbing documented so that you can at least mess with that. The user-agent selector will be based on the existing functionality that was restored in FPR17.
Assuming no major issues, FPR30 SPR2 goes live Monday evening Pacific as usual.
http://tenfourfox.blogspot.com/2021/02/tenfourfox-fpr30-spr2-available.html