Stuck in 'basic html view' in Gmail

I can switch to 'standard view' after I load it, but it keeps basic as the default. It used to have a place to change it, but it's not where it used to be and I can't find it. On Gmail's support page the advice points to a destination mine lacks, Quote:

settings->apps

. I use Firefox 68.6.0esr, the latest in Slackware.

Also, oddly, it won't let me 'delete forever' spam, telling me I can't do that when I'm 'offline' (I'm online, of course - I don't know what they mean when they use the word), but if I go into settings-offline, it tells me I have to use Chrome to go offline. There's also a destination in support which blocks me because I'm 'offline'.