I saw someone post somewhere that there's no hidden Add-on bar in Firefox 55 (that was an optional bar you could display in Firefox 4-28, not officially supported in Firefox 29+), so the old trick of extensions unhiding and using that bar doesn't work any more. If true, that could explain the problem.

If you check the Add-ons site pages for those extensions, do the authors mention or do the reviews mention any workarounds?

Status-4-Evar

One reviewer and a commenter on the developer's site say that the "beta" version works in Firefox 55:

https://addons.mozilla.org/firefox/addon/status-4-evar/versions/beta

I haven't tried it myself.

Hi Thanks for the answers. I just got another update, Fox Clocks is now on the top toolbar (under the tabs) which is helpful, a big thanks to those involved in solving this small problem. At the risk of heading in a slightly different direction, having all my add-ons/buttons etc and Fox Clocks in the same bar squashes things up a bit, is it possible (or are there plans) to have the option of adding a second toolbar. Thanks.

Have you considered placing the less-used buttons in the Menu Panel, so you can access them via the 3-bar button?

see the 1st screenshot as an example from Firefox 55"

the 2nd shows a mod that I did back in Firefox 38, which I am still using with that particular Profile - it works fine for the web activities I use that Profile for, I had too much poor compatibility with my installed extensions with S-4-E and CTR and just got used to the Australis UI, customizing the UI via "user code" to make it liveable for me.

I did that "stripping and reduction" via Stylish and userChrome.css / userContent.css - and haven't wasted my time with anything newer than Firefox 52, as with the loss of extensions and changes made to Firefox it's too much of a "moving target" to spend much time on it. I'll wait until (maybe) Firefox 60 for the changes to settle down. Or just use a different browser ...

edit: the ability to add a toolbar in Firefox is gone, too

Hi I have placed most buttons on the Menu Panel which helped a bit, the problem comes when I need 4 or 5 different time zones from Fox Clocks, they take up over half the length of the bar. I have it at a point I can work with it so although it isn’t ideal I can get by with this solution.

Thanks for the replys Barny.

Addition to what people said, add-ons will start breaking far more in the future if they are not written or adapted to the new Firefox API. Simply workarounds, even if not fully, work for the time being. I would invest time in finding alternative or waiting for devs to fully update their software.

Good news The issue has been resolved by an update...

A big thank you to the FF team.