I plan on ignoring the update for Australis for Firefox 29.0 in Mint. I do know about the add-on called Classic Theme Restorer, but I don't want to depend on lots of add-ons to make Firefox look like the present one in version (28.0).
Add-on authors sometimes don't support their add-ons in newer versions of Firefox. My favorite add-on is NoSquint and the maximum version number for Firefox now is version (27.0) which is on page 5 in the Add-on Compatibility Report in the link below.https://addons.mozilla.org/en-US/firefo ... all&page=5
I know SolydXK, when they update Solyd on April 15th, they have already planned to have in their repository, Firefox 24 ESR (extended support release) versions so Australis won't be seen until Firefox 31 ESR is released. If one chooses to use the Firefox 24 ESR versions in Solyd on April 15, it will automatically remove the usual looking and present 28.0 version and replace it with new ESR version of Firefox.
There is another Gecko based browser that is built on the Firefox 24 ESR versions of Firefox and that one is linux Pale Moon. It will not have the new Australis UI look and the author of Pale Moon says when Firefox 31 ESR is released, if the Australis UI is in these versions, he will fork Pale Moon. The author of the Pale Moon browser doesn't like Australis either because of all the things taken out of it (coding wise), like removing the Add-on bar and other things, to get ready for Australis. I use linux Pale Moon 24.4.2 as my default browser in both Mint and SolydX.