IE runs it perfectly. What do you hate about it?
I hate the file migrations / moves but otherwise it's powerful. The learning curve is awful but once you figure something out it's not that hard.
It's painful in my mind because of one specific company. I had to migrate their existing SharePoint ecosystem (about 18Gb of data and sites) into Office 365, prior to the 2013 update. Even using a 3rd party migration tool (ShareGate) it was a long and tortured process. Add on 50 users, all remote, and getting them configured...
The final kicker was when something broke in SharePoint. No idea what, but a few months after the Azure/2013 update, any users who were added to the permissions groups for a site collection weren't able to access it. All users who had access previously could use it. Any new account could not unless it was set as a global admin. Spent hours working on troubleshooting it with Microsoft and they finally said 'We have determined this is not fixable. Please replicate all sites in a brand new site collection.'
That, plus my boss keeps aggressively pushing it as a way to sync files to the cloud for law firms so lawyers can get them on the go. Too many headaches from that.