Not applying to all windows
First time I've noticed this: One of my windows is just showing up as "Mozilla Firefox." W7SP1, FF 57.0.4, CFT 0.1.5

What were you browsing there? I noticed FireTitle won't work on non-HTML tabs, like when opening a raw file here on GitHub (e.g. https://raw.githubusercontent.com/captnfab/FireTitle/master/firetitle/lib/lib.js)
Is this a limitation of the WebExtensions API?
Normal webpages—and it didn't matter which tab I switched to in that window. I've only noticed this once, though. (I also noticed it doesn't work when loaded under certain tab conditions, such as "Server Not Found"—but when I switch to another tab it works again, and remains working when I switch back.)
I regularly have FireTitle 'drop out', in the sense that the window either looses the assigned title or (possibly) never had it from the start. The way to (re)gain the title is to open the addons page. The probably mistaken impression is that of FireTitle 'crashing' and having to be reloaded. I shall try to pay more attention to when this occurs in order to give a better report.
Also if you open tab with HTML file from local filesystem the window always has title 'Mozilla Firefox'. It is very inconvenient.
Prefix not being taken into account on certain pages was a limitation of the WebExtension API. But it seems things have changed. On Firefox 58.0, Crappy Firetitle prefix is taken into account on the Modules page, on blank pages, on local html files, on view-source pages… Can you reproduce the bug with Firefox 58 ?
@khoroshilov can you still reproduce the inconvenient behavior you were reporting? If so, can you explain how?
@brokkr have you identified a way to reproduce the "crash"?
@captnfab sorry no, I stopped using the plugin shortly after as I found a way to identify windows associated with specific profiles by way of PIDs.
Ok good for you :)
@frasierlinde: were you able to find a deterministic way to reproduce the bug?
@khoroshilov can you still reproduce the inconvenient behavior you were reporting? If so, can you explain how?
Firefox 59.0.2 (Linux 64-bit) Crappy Firetitle 0.1.8 Title Pattern: nT
If active tab is http(s), all works just fine, but if I open a tab with html from local filesystem (file:///tmp/some.html) the title became 'Mozilla Firefox'.
I believe I am seeing similar, and is repeatable for me. Picture attached.
When a New Tab is opened, CFT is replaced by "Mozilla Firefox". This remains until I do something such as open a webpage, do a search (which leads to a search webpage), or click an existing Tab. The Title then reverts to CFT.
Frustrating when I switch to another window (Firefox, Office, or other app), before I do something to the New Tab (easily distracted). When I want to return to this previous session using Alt-Tab, the Window is not using the CFT name.
Firefox 60.0.1 Windows 10 Insider Build 17682 (After April Update, 1803, Build 17134) CFT v0.1.11
Lee~

It seems that the root cause is not local URL, but that the title is empty in html:
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8"/>
<title></title>
<style>
If I add some text between title tags, the firefox title becomes as expected.
Local files the same - Probably the same as above khoroshilov?
