Are you sure this isn't some Firefox add-on that you are using that is causing this? (E.g. uBlock Origin, Privacy Badger or activating Firefox's built-in anti-tracking protection or maybe just blocking third-party cookies; which could be solved by whitelisting the problematic webpages.)

I am using Firefox exclusively and I rarely find sites that don't work with Firefox after I disable blocking extensions.

Thanks for the suggestion, but I don't have any blocking extensions installed. If you use Notion you can check for yourself: there is no way to scroll down a page with the down arrow if the content exceeds the screen.

I've notice that some of the new fancy webapps that boosted of being write once run everywhere have issues in firefox.

Most notably is asana (it sometimes makes firefox use 100% cpu) and slack. Unfortunately we have slack at work but we're working to replace it as it has become increasingly bloated, user-unfriendly and buggy.

I would suggest reporting problems like these to https://webcompat.com

Volunteers will triage the issues and report them either to the site devs or Mozilla devs as deemed necessary.

I use trello in Firefox and haven't noticed anything that's broken. What specifically is broken for you?

Hm you're right. At some point I could no longer move lists around, but it's back now. It was the third UI to break after Intercom (customer replies not shown unless I reloaded) and Notion (down arrow does not scroll the page down), so I tried Chrome and it fixed the problem. Maybe I should have tried restarting Firefox...

Yes, I've found that now and then after a few weeks of heavy use without a restart, FF will become unresponsive in weird ways (refuse to open new tabs, or won't load URLs but already-loaded pages keep working, or won't allow you to drag links to other apps). It's a bit frustrating but a restart usually fixes that.

> if a UI is broken there is no choice but to migrate.

you also have the choice of not using the broken website

In general you would be right, but this is at work.

Yes. At work, principles don't apply.

> because the UI breaks in Firefox: intercom.io, trello.com, notion.so

This sounds like something you've done; do you have some weird extensions installed?

No. It's a work computer (Ubuntu 16.04) so I just use Firefox as is. I checked and the Trello bug was gone, but the Notion bug is still there: for content that exceeds the screen, the down arrow will not let you go down further than the visible content.

I recall using a very early version of tabbed browsing that arranged the tabs on the left by default instead of on top. I think this was Mozilla Browser on Red Hat Linux 6, around 2000. At the time, neither I nor my computer was able to handle more than one website at once, so I didn't use the feature much!