svg.elements.tspan - Firefox 137.0.2 does not support lengthAdjust / textLength attributes

[mikekaganski]

What type of issue is this?

Incorrect support data (example: BrowserX says "86" but support was added in "40")

What information was incorrect, unhelpful, or incomplete?

The MDN article claims full support for lengthAdjust and textLength attributes in tspan since FF 1.5. However, these are unsupported at least in FF 137.0.2. This may be seen in MDN playground https://developer.mozilla.org/en-US/play, where the following works fine:

<svg viewBox="0 0 200 60" xmlns="http://www.w3.org/2000/svg">
  <text y="20" textLength="5em">Small text length</text>
  <text y="40" textLength="150px">Big text length</text>
</svg>

but this doesn't scale text in FF (but works fine in e.g. Chrome):

<svg viewBox="0 0 200 60" xmlns="http://www.w3.org/2000/svg">
  <text y="20"><tspan textLength="5em">Small text length</tspan></text>
  <text y="40"><tspan textLength="150px">Big text length</tspan></text>
</svg>

What browsers does this problem apply to, if applicable?

Firefox

What did you expect to see?

The expectation is that both snippets shown above provide a picture like this:

Did you test this? If so, how?

As mentioned, the playground in FF shows the expected picture for the former snippet, but this for the latter snippet:

Can you link to any release notes, bugs, pull requests, or MDN pages related to this?

https://bugzilla.mozilla.org/show_bug.cgi?id=890692

Do you have anything more you want to share?

No response

MDN URL

https://developer.mozilla.org/en-US/docs/Web/SVG/Reference/Element/tspan

MDN metadata

MDN page report details

• Query: svg.elements.tspan
• Report started: 2025-05-30T12:23:04.703Z

[caugner]

Confirmed with this JSBin.

Let's update the Firefox support statements to { version_added: false } along with the mentioned Firefox bug as impl_url here:

browser-compat-data/svg/elements/tspan.json

Lines 211 to 213 in e606ffb

	"firefox": {
	"version_added": "1.5"
	},

browser-compat-data/svg/elements/tspan.json

Lines 211 to 213 in e606ffb

	"firefox": {
	"version_added": "1.5"
	},

@mikekaganski Would you like to open a PR with these changes? 🙏

[mikekaganski]

Would you like to open a PR with these changes?

No thanks; that's your change, I would only copypaste it :-) so it's in no way would be mine. I appreciate your confirmation, and your offer, though :-)