I don’t know about that. I think no.
I got the same problem since friday last week.
The browser is totally unresponsive, Even reinstalled the app but did not make any difference
A couple of related bugs which might help:
- https://bugzilla.mozilla.org/show_bug.cgi?id=1706219
- https://bugzilla.mozilla.org/show_bug.cgi?id=1685780
Although they seem focused on windows.
I see that @Dmitriy_Ermolaev uses a localized version of the browser. @thomas_henry & @1010189296 are you using the default english version or another locale?
Mine is in Dutch, indeed 
Is the Englisch version somewhere available so I could test this? 
I would assume that this should give you the English version: https://download.mozilla.org/?product=firefox-devedition-latest-ssl&os=osx&lang=en-US
Also, I use the en-US or the en-GB version (have to check) and had no issues in the last days, but will monitor and post here if I see something similar.
Thanks, I’ll figure it out. Twitter is very slow in Russia due to political restrictions. Temporarily rolled back to version 74.0b6.
ah, let me include the content here:
type “about:support” (without quotes) on your address bar, hit the “Refresh Firefox” button in the upper-right corner, and confirm it
it’s about:support (no space, no semi-colon at the end)
I think I found the preference responsible for the bug: browser.uiCustomization.state.
If you can locate your profile directory, open prefs.js and delete the corresponding line.
Eg on a local profile it was
user_pref("browser.uiCustomization.state", "{\"placements\":{\"widget-overflow-fixed-list\":[]},\"seen\":[\"developer-button\",\"profiler-button\"],\"dirtyAreaCache\":[],\"currentVersion\":16,\"newElementCount\":0}");
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I think I found the preference responsible for the bug: browser.uiCustomization.state.
I’ve encountered this issue on Windows and not Mac OS, but I can confirm that deleting this pref solves the issue for me.
This was the value:
user_pref("browser.uiCustomization.state", "{\"placements\":{\"widget-overflow-fixed-list\":[]},\"seen\":[\"developer-button\",\"profiler-button\"],\"dirtyAreaCache\":[],\"currentVersion\":16,\"newElementCount\":0}");
If it helps, I can also send you my profile folder backup if there is anything else in there that would indicate more.
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I’m having the exact same issue. I first noticed it when trying to work on a client’s website this morning. I am running MacOS 10.14.6.
Where do I access the preference value? Trying to use about : support didn’t do anything.
You can find your profile folder following the instructions on https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data#firefox:mac:fx89
(see the Finding your profile without opening Firefox section)
Once you have your profile folder located, there should be a prefs.js file inside of it. Open it with a text editor of some kind, find the line containing browser.uiCustomization.state, and delete the whole line.
After that, you should be able to start Firefox Developer Edition again.
Hopefully this is just going to be a temporary workaround and we can rollout a fix very soon.
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Thanks a lot to Julian Descott !!
This worked for me.
Same here! thanks a lot @jdescottes ♂
Will this be applied for ever or should we do this on each update? 
Happy to see that you are unblocked!
Will this be applied for ever or should we do this on each update?
The migration code responsible for this issue has now been identified and fixed in https://bugzilla.mozilla.org/show_bug.cgi?id=1706219
The patch should quickly reach Nightly, and I’m sure we will push it to Beta & Developer Edition very soon.
The manipulation will no longer be needed after that.