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Hello! My Firefox browser is currently in a state where all fonts/letters in the Firefox interface (bookmark bar, settings, about page, website name...) are replaced by undecipherable characters.

I've searched for similar problems already and tried so far the following steps to resolve, unsuccesfully...

• Opening the browser in Safe Mode / Deactivating all extensions
• Uninstalling and reinstalling Firefox

• Disabling hardware acceleration
• Trying on another profile




When I copy paste said text to another window (ex: Notepad, Chrome Browser…) it appears properly. And as you can see in the screenshots below the text in actual websites is readable -- only the browser's interface, setting, address bar... are scrambled.

Does that bug rings any bell? Do you have any other troubleshooting steps I should try to resolve this? Any help will be appreciated! : )

Sending of the message failed. An error occurred while sending mail. The mail server responded: <anonymous@[10.0.0.31]>: Sender address rejected: not owned by user a1.914306843. Please check the message recipient "christine.krieger@a1.net" and try again.

why do I get this on new download

Had my laptop serviced at Best Buy, but upon booting it up the icon for 1Password in the upper tool bar was missing. Trying to figure out how to add it back. I use Mozilla Firefox and have Windows 11.

As of September 3, 2026 all my new emails are going into a random folder instead of the inbox. This is also happening on my wife's PC plus and we are not getting the emails to our iPhones until we get out of Thunderbird. What has changed? This has not happened before.

I've been using Thunderbird on Windows 10 since last year sometime. Currently I'm on version 151.0.1.

I've 4 x mailboxes here and since yesterday, 3 of them show me an unusual message when checking for emails. I tried attaching a screenshot but although the screenshot uploaded, I couldn't find a way to insert it here. But the message says Unable to write the email to the mailbox and asks me to check if I've write privileges (which I have) and to cheek the available disk space.(currently 101GB free).

The message is happening 2 or 3 times each day and lasts for about half an hour, then everything works fine again. Has anyone else seen this??

My hardware is low end from 2016, Pentium 3825U, HD Graphics, and 4gigs of RAM. In the old times, the browser was fast, but this year it has slowed down so bad. I needed to switch to Thorium browser because Firefox became so heavy, using too much RAM and CPU. Please make the browser light, fast, and good for old systems again! (I want to use Firefox back)

My font on some sites is being forced to this horrible condensed font and it's seemingly nothing to do with my font settings in browser. Thing is, I VAGUELY remember changing a setting SOMEWHERE to actually do this, but it's not the main font setting in accessibility. Furthermore this issue has only started happening in the last day or two and my vague memory of setting my font somewhere was years ago.

Is there any other setting in Firefox that affects default font for certain sites?

[Images attached from terraria.wiki.gg in a normal tab (with bad font) and private browsing tab (with the font it SHOULD have) for comparison]

(AI written summary of troubleshooting steps taken before making this support thread)

Firefox version: - 152.0.1 Release - 153.0 Nightly

OS: - Windows 11 build 26200

GPU: - NVIDIA GeForce RTX 4070 SUPER

Codec package: - Microsoft HEVC Video Extensions installed from Microsoft Store

Problem

Firefox does not expose HEVC playback support, causing Twitch to disable 1440p streams encoded with HEVC.

The same machine can play the same HEVC Twitch streams in Chrome immediately after installing HEVC Video Extensions.

Expected result

Firefox should report HEVC playback support and allow playback of HEVC streams, as Chrome does on the same system.

Actual result

Firefox reports HEVC as unsupported.

about:support:

codecSupportInfo: H264 SWDEC HWDEC VP9 SWDEC HWDEC VP8 SWDEC HWDEC AV1 SWDEC HWDEC HEVC NONE

Troubleshooting already performed

- Installed Microsoft HEVC Video Extensions - Rebooted Windows - Updated NVIDIA drivers - Verified hardware acceleration is enabled - Tested with a brand new Firefox profile - Tested with Firefox Nightly - Confirmed Chrome can play the same HEVC streams

Additional observations

Chrome: - Twitch 1440p becomes available immediately after installing HEVC Video Extensions - Twitch Stats for Nerds reports:

 hev1.1.6.L150.90.0.0.0.0.0

Firefox: - Twitch reports that the browser does not support the required resolution - 1440p remains greyed out - about:support continues to report HEVC NONE

Reproducible tests

Firefox console:

MediaSource.isTypeSupported('video/mp4; codecs="hev1.1.6.L150.90"')

Result: false

MediaSource.isTypeSupported('video/mp4; codecs="hvc1.1.6.L150.90"')

Result: false

navigator.mediaCapabilities.decodingInfo({

 type: "media-source",
 video: {
   contentType: 'video/mp4; codecs="hev1.1.6.L150.90"',
   width: 2560,
   height: 1440,
   bitrate: 8000000,
   framerate: 60
 }

})

Result: {

 supported: false,
 smooth: false,
 powerEfficient: false

}

For comparison:

MediaSource.isTypeSupported('video/mp4; codecs="av01.0.08M.08"')

Result: true

navigator.mediaCapabilities.decodingInfo({

 type: "file",
 video: {
   contentType: 'video/mp4; codecs="av01.0.08M.08"',
   width: 2560,
   height: 1440,
   bitrate: 8000000,
   framerate: 60
 }

})

Result: {

 supported: true,
 smooth: true,
 powerEfficient: true

}

Additional note

Setting:

dom.media.webcodecs.h265.enabled = true

causes HTML5 codec test (https://html5test.co/) to report H.265 support, but does not change:

- about:support - MediaSource.isTypeSupported() - MediaCapabilities.decodingInfo() - Twitch HEVC playback availability

Question

Is this a known issue with HEVC Media Source Extensions support on Windows 11 build 26200, or is there another requirement for Firefox to expose HEVC playback capability through MediaSource and MediaCapabilities when the Windows HEVC codec is installed and functioning in Chromium-based browsers?

It is not a problem, but I would like to know why did my Firefox app (phone) change its logo and name to "Firefox Preview". Was it me that accidentally activated it?

Thanks!

After updating from Firefox 154 to 155.0 on Windows 11, the download progress indicator on the Windows taskbar icon no longer appears at all.

What I see: - While a download is in progress, only the circular progress on the in-window Downloads button is visible. - There is no progress bar/fill on the Firefox taskbar icon, even when the window is focused and the Downloads panel is open. - In Firefox 154 this taskbar progress worked. - Chrome on the same PC still shows download progress on the taskbar correctly.

I checked about:config for anything related to taskbar/download progress and found nothing that controls this.

Is the Windows taskbar download progress still expected to work in Firefox 155, or was it removed/changed? Has anyone else noticed this?

Thanks.

I installed Thunderbird on my new laptop, then imported the profile from my old laptop

The main screen has, under "Inbox", folders for Drafts, Sent, Trash, Archive and Spam, which are being used by the program

Folders for Drafts, Sent and Trash also appear under "Local Folders" (along with Outbox) and these aren't being used by the program.

How do I get rid of these duplicate folders? "Spam" had a delete option, so that was easy, but the others don't.

I tried the two suggestions for a previous "Duplicates" question but they didn't resolve things.

Thank you

Since the last update (I know that Firefox DE is a beta/semi-nightly release, I just want to know if this is my mistake or a bug), only my first firefox window has address bar, all the other windows don't. And when tabs are vertical, the rest of the windows don't even have a title bar. (This behavior doesn't apply to newly created windows) Also, non-primary windows also lose the capacity to resize the vertical tab bar. ¿Did I do something wrong or is this a bug?