Steps to reproduce:
- Be me, or one of several other people, but not James F. (This step may be difficult to reproduce. ;-)
- Login on Firefox.
- Try to open an article in VisualEditor.
- Wait. Wait. Wait. Wonder why a page that pops open in Safari in less than five seconds still hasn't opened in Firefox despite the animated blue bar showing for more than 30 seconds now.
- Wait. Wait. Wait. Wonder if this is ever going to open.
- Give up and reload. Maybe it works this time; maybe it doesn't. If it doesn't, consider restarting Firefox. That usually helps... for one article. Then it goes back to its old behavior of occasionally opening a page, but not usually.
I don't feel like I have a lot of useful information to give you, but this has been a problem for a couple of weeks and does not seem to be getting better. Logging out may help, according to https://en.wikipedia.org/w/index.php?oldid=608667917#VE_does_not_start