Browser Toolbox' Style Editor randomly changes text while typing

Browser Toolbox’ Style Editor will frequently randomly delete the characters I have just typed while I’m still typing, and the cursor will move. (I was editing userChrome.css.)

Ctrl-Z, or Undo from the context menu, will move the page to the top.

It happens starting from the (current) version 82.0 of Firefox (stable release). It didn’t happen in the previous version. It also happened in the Developer Edition of Firefox.

Is it a bug, or can this be prevented?

Hello, I have the same problem and it is very annoying, because I use this Style Editor daily and it makes me crazy. I’m thinking about downgrading or moving to Chrome until it is fixed. I cannot work with this version of Firefox. I spent much more time developing new codes than ever before.

I am also having this problem. I can temporarily fix by closing the style editor, reloading the page I’m on and reopening the tools but the problem inevitably returns. I’m on macos catalina 10.15.7 and firefox v 82.0.3. (as I looked up the version I see an update to v83. I’ll apply and see if that does anything.

i can confirm that this continues to happen in the latest version of firefox v83.0 (64bit) for mac.

Having same issue on Ubuntu 20.04 LTS and Firefox 83.0 (64bits).

Hello folks,

I tried to reproduce this issue without any luck so far :confused:
Is there any specific steps that lead to this behaviour?

For me is just open the style editor, work on it and in between refresh the page with the inspector always opened. Do it a couple of times and the problem starts (Removes what you are typing).

Still no luck.
Is this happening on every website (even something like data:text/html,<meta charset=utf8><style>h1 { color: blue; }</style><h1>Hello</h1>) ?
Can you reproduce it on Firefox Beta and/or Firefox Nightly as well?

Thanks a lot for your answers

I think had this issue the other day in the Browser Toolbox (experimenting with editing a file imported into a userChrome.css file). It seemed there was a problem with the autocomplete feature where I would type/paste something, see the list flash up and ignore it, but after a beat my text would be erased or replaced. When autocomplete didn’t come into play, nothing abnormal happened. I haven’t figured out whether there is a pattern to it; I’ve probably only seen it three times this year.

Tested in Firefox Nightly 85.0a1 (2020-11-24) (64-bit). Same exact issue.

yes it does, Firefox developer 84.0b4 (64-bit)

If anyone has good steps to reproduce, we have a bug on file for this at but so far no one in the DevTools team has been able to reproduce the issue.

Been happening to me for a while now. Seems to be fine most times, then somehow it gets triggered and gets really aggressive with auto-correcting by deleting perfectly good code. Then I have to reenter the same code three or four times before it remains. Would love to see this go away without having to disable auto-correct.

This has been happening to me for a while now, good to know I’m not going nuts.

I can also confirm this is an issue. Oddly, when I switch Firefox into safe mode the problem happens less frequently. I also wonder if the speed at which I am typing has anything to do with it.

I can also confirm this issue. OS: Manjaro + xfce4. It happens in both Firefox standard and Developer Edition.
And a second observation (i do not know if related to this above) is that sometimes after a page reload the source list files in debugger appears empty. After a browser closing an restarting procedure is all again fine, but sadly only for a short time.

I have this same problem for a good few months now, I’m running Win 10 with Firefox version 84.0.1. The autocorrect / auto format for the CSS code in the style editor gets super aggressive and will delete my code as I am midway through typing even the first element without errors (e.g. “display:” is as far as I get and it deletes it). Please can you give us an option to disable the auto-formatting of CSS in the Style Editor?

The issue is now fixed in Firefox Nightly (86) and will be in beta/DevEdition in ~3 weeks (and in release a month after).
We can probably try to uplift the patch so it reaches beta (and this release) earlier

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OMG! Firefox Version 85.0b8 (64-bit) and this issue is still there, can any do something? My entire work depends of this toolbox and I’m having a lot of problem to code CSS styles.

As said in my previous message, the issue will be fixed in Firefox 86.
If you’re heavily impacted by this bug, you might want to download and use Firefox Nightly

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