After I had to restart the laptop for something else, I then found in Firefox that that gap between the 'save to pocket' and 'open menu' icons was no longer there. Previously there definitely was a gap because when I floated the mouse over it, that hidden and disabled 'Firefox Screenshots' icon was revealed.

1. Firefox 55.0.2
2. Firefox 55.0.3

1. Index of /pub/firefox/releases/55.0/win64/ Type Name Size Last Modified; Dir. Dir: ach/ Dir: af/ Dir: an/ Dir: ar/ Dir: as/ Dir: ast/ Dir.
2. Note: Firefox 55 is the last version that supports devices running Android 4.0; 55.0.1 August 10, 2017 Desktop. Off-cycle stability update. Fix for a rendering issue with some PKCS#11 libraries. Fix for a problem causing What's new pages not to be displayed. Fix for a regression in the tab restoration process. Disabled the predictor prefetch.
3. Mozilla Firefox 64-bit for PC Windows. Mozilla Firefox is an open-source browser, which launched in 2004. Its simple and easy to use, with an excellent UI and in-built features. It is a popular browser with developers and has an active com.
4. Thank you, everybody. I tested the code snippets here on the recent browsers: Chrome 55, Firefox 50, IE 11 and Edge 38 and I came up with the following combination that worked for me for all of them. I'm sure it can be improved, but it's a quick solution for whoever needs.

Firefox 55 and Selenium IDE

The bad news: from Firefox 55 onwards, Selenium IDE will no longer work.

The reasons for this are complex, but boil down to two main causes:

1. Browsers are complicated pieces of software that are constantly evolving. Mozilla has been working hard to make Firefox faster and more stable, while still retaining the flexibility and ease of extension that we’ve come to know and love. As part of that process, Firefox is switching extensions from the original “XPI” format, to a newer, more widely adopted “Web Extension” mechanism.
2. The Selenium project lacks someone with the time and energy to move the IDE forwards to take advantage of the new technologies.

Selenium is one of the most widely used pieces of testing software there is. Despite this, the team of people regularly contributing is small: since the start of the year, there are only 11 people who have made more than 10 commits, with two people accounting for more than half of those. Since 2016, only one person has been maintaining the IDE.

Selenium is an Open Source project. None of the core contributors — not the IDE maintainer, not the language binding owners — are paid to work on work on it. They do it because they love working on the code, and they typically do it in their “copious free time”. The IDE maintainer has had almost none of that to spare. We should all be thanking that committer for his time and effort. Thank you, Samit!

Firefox 55.0.2

So what can we do to move forward? The first thing is that there are now a wealth of tools that are stepping up to fill the gap. You should go and have a look at them. The second thing is that there is an effort to rebuild IDE using modern APIs, to be usable across more than just Firefox. The fine people at Applitools are helping with this effort.

The third thing? That’s you. You could help us.

Firefox 55.0.3

If you believe that a friendly UI for quickly recording and playing back tests is a useful Open Source tool, then please come and join us! The main technical discussions are happening on the #selenium IRC channel. If you’d prefer Slack, you can join us on that too. Or there’s the ever useful selenium-developers mailing list. Come onboard. We’d love your help, and IDE is a wonderful thing to contribute to!