Firefox 153 will force a major sidebar downgrade on everyone next month

Mozilla is nuking the classic Firefox sidebar permanently on July 21. Release 153 will pull the plug entirely, deprecating the legacy UI flag and forcing everyone onto a redesigned interface that wastes a good chunk of horizontal screen real estate.

I bounce between browsers a lot, but Firefox’s old sidebar was always the gold standard for pure, unadulterated information density. You hit a shortcut, a barebones list pops out, and you use the top dropdown to swap between bookmarks and history. It just worked. Now it’s a bit of a mess. The updated version trades that utilitarian dropdown for a chunky, icon-heavy vertical pane. So while this doesn’t really bother me all that much when I’m on my PC paired with a 4K 28-inch monitor, you can expect it to swallow some screen space on smaller displays or ones with lower resolutions.

That explains why power users are miffed, to put it lightly, with the change.

Over on r/firefox, users who’ve just got the update are realizing the new implementation breaks decades-old muscle memory. Dragging a history entry into the tab bar to open it in the background? Gone. Selecting multiple non-consecutive links with the Ctrl key and spacebar to batch-open them? Borked. The new UI just hijacks focus and instantly loads the page the second you hit the spacebar.

A giant downgrade.

You can’t even escape it if you prefer vertical tabs. I dug into the latest stable build looking for a clean opt-out. There isn’t. Navigating to Settings > General > Browser layout and toggling off ‘Show sidebar’ instantly forces the browser back to a horizontal tabs layout. Toggle vertical tabs back on? The chunky new sidebar resurrects itself immediately. They are hardwired together at the core level.

For reference, here’s a screenshot before I toggled on vertical tabs.

Here’s a screenshot after I toggled on vertical tabs.

Basically, Mozilla is giving users an ultimatum. You either swallow the wasted pixels, or you lose vertical tabs entirely just to keep a semblance of the classic UI.

Support staff on Mozilla Connect confirmed the Q3 death date while promising patches for regressions like the broken multi-delete history function. Until those ship, you’re stuck manually right-clicking every single link you want to clear.

Featured image generated with AI

We stand out from the tech-media crowd because we break news stories; we mainly bring you stuff that you won’t find anywhere in the mainstream tech media. Our stories have been picked up by some of the world’s most popular websites and media outlets—more info is available here.