Debian is stable. This means, once frozen, only security updates and targeted fixes are accepted. New versions are not supplied by default. An exception is if you enable the -backports repository which grants access to some new versions of software, compiled against its stable dependencies. But things usually only go into -backports if there is interest in that. firefox is not in backports. Not sure if there's a reason besides lack of interest. Most sites do not require the very latest version of a browser so only a few people will have had your experience.

Also, this is an interesting read which helps explain the stable philosophy: wiki.debian.org/…

@Stewart browsers are the exception to this rule; new upstream releases are allowed into Debian stable. Preferably from a “long-term support” branch if possible (as is the case for Firefox), but not necessarily — Chromium tracks the latest release in Debian stable too.

To be fair, while I completely agree that this looks scary, it isn't actually all that complicated. You're absolutely right that it isn't reasonable to expect your average computer user to do this, but for someone who is used to the command line, it isn't that bad. So while it does seem like something Debian should fix, for you personally, I would suggest you just do it. All of these commands are safe to copy/paste directly into a terminal, so it is a matter of running 7 commands (6, really, if you don't feel the need to verify the signature manually).

At home, I have chosen Firefox, Debian, I can uninstall it and reinstall it through six lines of bash commands, that's true. At work, it's not sure. For many users it won't be convenient to do so: it's the apt job, after all, to manage such command lines. Whatever, the change request is submitted : bugs.debian.org/cgi-bin/bugreport.cgi?bug=1082590

"learned that my Firefox version wasn't supported anymore since September 2024, 1st." - It's worth noting that that message is outdated/incorrect; Firefox 115 ESR support has been extended to March 2025, see the Firefox Release Calendar

@marcelm If Slack website publisher warn so, I tend to trust them. And if a 128 ESR version is available that complete the conditions to replace the current 115 one, it's the normal path to upgrade to it. What's the interest of slowing down or to put some obstacles in this process? You might consider that I'm asking this upgrade early, but it has chances to avoid to users unexpected incompatibilities if it is done now, when it's possible.

@MarcLeBihan Regardless of what Slack says, Mozilla has extended Firefox 115 ESR support from September '24 to March '25.

@marcelm The problem is that some web sites declare that Firefox 115 esr cannot (= is unable to) handle them correctly. Firefox can have an extended support by Mozilla in its 115 version, what's the use if it doesn't display/handle some web pages correctly? I see no good reason to avoid upgrading it to 128 esr now.

@marcelm it’s supported until March only for old versions of Windows and macOS (which doesn’t contradict your point re Slack, but it doesn’t help on Linux, and not just for Slack).

Incidentally Slack works fine for me on 115esr...

@StephenKitt Did you saw a warning telling that your Firefox wasn't maintained anymore? I had it the two first times I came, then it disappeared. I cannot login further into Slack yet, but this is due to a change about groups I don't understand yet. So I can't tell more: I'm just relying on the warning message I saw to ask for this upgrade. But on the issue I've opened, one added another web site that causes a problem: "chatgpt.com, which uses the Intl.Segmenter introduced in version 125. Currently, it's impossible to log in and, if you're already logged in, the page won't fully load."

I get a warning about Slack being unsupported on Firefox 115, not about Firefox not being maintained. That’s what the message you’re showing means: that Slack won’t support this version of Firefox. It doesn‘t mean that this version of Firefox is no longer maintained.

@StephenKitt Yes, sorry for the mistake →not supported. I've just entered my slack group, and it seems to work, I agree.

@MarcLeBihan Ah I see, that was a misinterpretation on my part, since Mozilla originally planned to end support for 115 ESR in September 2024 as well, but that has been extended. I did not intend to make a claim on what browsers slack supports.

@StephenKitt Do you have a source for that? I understand they'll only be offering builds for old Windows and MacOS, but Debian makes their own builds from source anyway.

Although not a proper long term solution, if the core problem is that Slack has announced they're going to stop running on FF 115 out of a policy/whim (instead of actually starting to use a browser feature that doesn't exist in 115), you might get some temporary relief rather easily by spoofing the FF version indicated to the site using a suitable browser extension such as Custom UserAgent String. Chances are it may buy you the time to arrange for a proper upgrade, more so since Slack still seems to work even with an unmodified 115ESR.