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I routinely record short screencasts with Kazam, and I can't watch my own videos after posting them on sites like GitHub because Firefox says "Video can't be played because the file is corrupt". Or for example when I upload them to sites like ezgif to convert them to a GIF, which works just fine because, well, the file is not corrupt. Other browsers like Chromium play them just fine.

Apparently the "OpenH264 Video Codec provided by Cisco Systems, Inc" is properly enabled in my system. This has been happening to me for months or years, but only today I decided to open a thread here.

There are two things here:

1. Firefox can't play the file. I'm sure there's some sort of misconfiguration on my side, or bad defaults, or a missing plugin, or similar. 2. Firefox shows a misleading message. The file is not corrupt! The root cause is something else.

Any advice on how to fix the first one?

I'm using 64-bit Linux Mint 20.3 LTS, and the latest version of Firefox from the repositories (101). Suddenly, for no reason I know, my default profile has started crashing immediately on trying to run Firefox. A small window comes up with the error message

XML Parsing Error: not well-formed Location: chrome://browser/content/browser.xhtml

     <button when-cofnection}"secure-cert-user-overridden"="" <="" pre="">
and then a line of ------^  where the ^ indicates between the t and the i of cofnection
Yes, I emphasise that I HAVE copied the error message carefully, including the mismatched bracket pair and the cofnection rather than (I assume) connection
I've managed to get a working version of Firefox by creating a new profile and using that (as in for posting this request for help), and I do have a recent backup of my bookmarks, but it will be a royal PITA if all my logins and passwords have disappeared. I don't want to go any further than this without some guidance, as all the messages I've found detailing how to fix this seem to make the assumption that I'm running Windows. 
Can anybody help, please?
</button>

I’ve not had much success with my online searches to learn the details about what takes place when Firefox syncs browser information across devices. To keep things simple, assume I interested only in syncing bookmarks and staying within the Firefox environment, i.e., no syncing to another browser. Please note that I am NOT asking for help in setting up Sync on different devices or in how to turn Sync on and off. Rather I am seeking help to understand what “sync” means, that is, the details of the sort of information transfers that take place between individual devices and the Firefox Sync server.

Here’s what I currently understand. After signing in to my Firefox account on Device 1, setting up syncing on that device, specifying that I want only bookmarks to be synced, and turning syncing on, the set of bookmarks on Device 1 is sent to be stored on a Firefox server. After that, whenever one is signed in to the Firefox account on Device 1 and syncing is turned on, any changes to the bookmarks on Device 1 will "automatically" (but I don't know how quickly) end up being reflected in the set of bookmarks stored on the server. Fine so far.

In addition to Device 1 I have another device, Device 2 which has not been set up for Firefox Sync. It has its own set of bookmarks. Some of them are also on Device 1, some are not. I sign into my Firefox account on Device 2 and set up syncing on it. I follow the steps for doing this in https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer, “Connect additional devices to Sync.” I then click Sync Now. OK, now what happens?

1A. Do the bookmarks in Device 2 get added to the bookmarks stored in the Firefox Sync server? 1B. Do the bookmarks NOT in Device 2 get deleted from the bookmarks stored in the Firefox Sync server?

OR

2A. Do the bookmarks stored in the Firefox Sync server get added to the bookmarks in Device 2? 2B. Do the bookmarks NOT stored in the Firefox Sync server get deleted from the bookmarks in Device 2?

After whatever transfers of bookmark between Device 2 and the Firefox Sync server take place, and assuming that I’m still signed in to my Firefox account on Device 1 and that syncing on that device is still turned on, what sort of transfers of bookmarks takes place between the new set of bookmarks stored in the Firefox Sync server and the set of bookmarks already on Device 1?

3A. Do the bookmarks then present in the Firefox Sync server get added to the bookmarks in Device 1? 3B. Do the bookmarks no longer in the Firefox Sync server get deleted from the bookmarks in Device 1?

Finally, what happens to the set of bookmarks in Device 1 and Device 2 if I’m simultaneously signed in to my Firefox account, syncing is turned on in both Devices 1 and 2, and a bookmark is a) added to either device OR b) deleted from either device?

I’m sorry this message is so long, but I’ve wanted to be clear about the things I don’t understand in regard to Firefox Sync. I’d really appreciate what anyone can say to help me clarify these points. Thanks so much.

For the past few weeks I've been receiving numerous firefox crash reports & also when trying to open firefox an error indication that firefox is already open. I've never had this problem with firefox in the past, and have been an avid firefox user for many many years.

This occurred on my old desktop computer which died this week & is also occurring with my brand new, out of the box HP laptop computer (with ALL the windows updates and HP updates installed); The old computer used Windows 10 Pro, the new computer uses Windows 10 Home.

My old computer used just the windows defender for protection, but my new laptop comes with a 1 month trial of McAfee which I am using until the trial expires.

Firefox is (and was) my default web browser. The software and updates for firefox have always come from your official website and in a timely manner.

Could you please look into and resolve this issue?

Thanks so very much for being Mozilla Firefox!

I have Firefox 101. It is set to open previous session tabs but it does not. Further I am not able to retrieve the ones I used to have available when I open Firefox. I have not cleared the history.

How to import passwords from a CVS file (such as create by Keeper password manager) into Firefox Version 101?

I looked at older questions (example: <<https://support.mozilla.org/en-US/questions/1329981 >>) but the solutions do not apply to the latest Firefox version.

Thank you in advance for your help

The videos look blurry and it seems like a little zoom part can be seen from one corner of the video to zoom in more. The whole video is not controlled within the skin. Nothing in the video can be seen after playing the video due to problems. I have started the application by deleting it several times in a row. In the first case it stays good for a few days and then it causes problems in video play. After browsing all kinds of websites, the videos get blurry. Hopefully that will solve the problem.

Please see https://support.mozilla.org/en-US/questions/1311330 That solution does not work for me. Mac Pro with M1 chip running 12.4 Thanks!

Hi all. Did a search but found nothing that helped. Just updated my Fedora 36 workstation and tried to play videos in CNN and MSNBC web sites and get the error message: "Code: 4 | Message: Something went wrong during native playback." I am using the latest Firefox WEB browser. UTube videos are playing fine. Someone has stated on the Fedora forum that they have the same problem but has no problem in Chrome on the same machine. Any ideas? Thanks in advance. Bob BTW, this happened in two machines running Fedora 36 and Firefox 101.0.

Wenn ich den Firefox Browser starte und surfe und nach einigen Sekunden hängt sich der ganze Browser einfach so auf! Wenn ich Firefox dann schließe und wieder öffne dann wird mir das Firefox Logo ein paar Sekunden angezeigt und dann wird die eigentliche Webseite geladen die vorher sich aufgehängt hat. Bitte beheben.

I was using Firefox on windows 10 laptop, everything was synced with my account. Now after switching to Ubuntu I can't see my bookmarks, Just an empty toolbar. Now I don't have access to my old laptop, I sold it.

Any help?

as of yesterday 6-10 i cannot sign into this site https://maps.harley-davidson.com/ I've tried disabling all the security i could think of. i can sign in if i use Microsoft edge or if i put fire fox in trouble shoot mode. in troubleshoot mode i can sign in but the site will not display anything. this was working just fine until yesterday Ive made no changes to anything. please help

Hi guys. So, I have Avira free antivirus. Can I still install for example Norton web security addon for Firefox? Will there be any problems between my installed antivirus and the Norton addon? Sorry if this is a noob question, but there you go :) Any help would be appriciated. Thanks in advance for any reply.

Getting error SSL_ERROR_BAD_CERT_DOMAIN on all my sites that are signed with a SSL Cert from my internal CA since updating past version 99

This appears to be a bug starting after Firefox version 99 on Windows because after i upgraded to Firefox version 100 i started getting this on all my SSL Certs from my CA and they worked fine prior to the update. Can anyone confirm if something changed after version 100 that is causing this?

Thank you.

I've been using Firefox almost exclusively for years now, and it's always worked flawlessly - until recently! Now, when I log into my GitHub account, I can no longer edit and commit my changes.

When I click on the "pencil" on a rendered page, I am taken to the "edit page" where I can make my changes (in markdown), preview those changes (rendered in markdown), and then commit those changes. Beginning very recently (within the past few days), the preview tab is no longer functional, and I can no longer commit my changes to the file.

I've verified that GitHub has not changed their interface by logging in from my Chrome browser, and following the exact same procedure used in Firefox everything works as it always has.

I recently upgraded from ver 99 to 100, and now to 101.0.1. I recall clicking a pop-up immediately after the 99-100 upgrade that had something to do with cookies... sorry, I know that's lame, but it's all I can recall now. In any case, I am certain this happened recently.

Please help... I have to use Chrome for a couple of things already (my brokerage account at Vanguard for example), but I despise Google, and want to limit their spying.

Thanks,