Does anyone have contact details perhaps for Shivanand? If we can contact them directly, in case they've not seen the proposal above, this can at least give us an idea on getting a fix at least for the multi-process bug. I would genuinely be happy to donate to a paid version if this kept the add-on alive, as I've found no alternatives to this. (Sadly I don't have the apptitude to teach myself coding to make one myself!)
There is another option that no-one seems to have mentioned here, that I could see at least: using Waterfox and disabling multi-process.
Waterfox is a fork of Firefox which still supports all legacy add-ons. I'm presently using the last-know-working version of ColorfulTabs (31.2.3) from the Classic Add-ons Archive.
Shivanand: Is there any chance you might consider doing the following?
- Continuing to develop the legacy add-on for Waterfox / Firefox ESR users?
- Fixing the bug in the legacy add-on with multi-process?
Suffice to say, I'd be willing to donate to the development of this. I think others using Waterfox would too.