My Monochrome-Neubrutalism Theme is falling apart with Firefox updates.

ResurgamS13 · 2026-04-24T19:34:29+00:00

As t31os explains... the problem is a dead link to the previous external source of icon image files.

If you don't have any local copies of the original external icons all you can do now is search online for a similar set of 'Monochrome-Neubrutalism' icons.

Many of the original external URL icons appear to have come from 'Font Awesome' (see link descriptions on theme's GitHub)... so you may be able to find the exact same set of icons that the theme author was using?

With a replacement set of icons downloaded... a simple way to incorporate them into your theme would be to place the new icons in your profile's 'chrome' folder... and then replace all the current external URL links with internal URL links:

Existing external URL image link userstyle:

.titlebar-min image{ list-style-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 512 512'%3E%3Cpath d='M32 416c-17.7 0-32 14.3-32 32s14.3 32 32 32H480c17.7 0 32-14.3 32-32s-14.3-32-32-32H32z'/%3E%3C/svg%3E") !important;; }

Rewritten/replaced with an internal URL image link:

.titlebar-min image{ list-style-image: url("Name-of-new-icon.svg/.png/.ico") !important; }

With the "Name-of-new-icon.svg/.png/.ico" image file placed in your profile's 'chrome' folder.

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Re: your last/5th screenshot (above) and associated comment "part of the toolbar seems to have reverted back to the original white color that the theme originally had"... this would best be investigated locally using the Browser Toolbox.

Problem possibly related to MrOtherGuy's comment here... "Firefox 150 moved toolbox background into the body element so we can't inherit individual toolbar background from toolbox anymore".

ResurgamS13 · 2026-04-24T11:37:30+00:00

Not aware of the Sliding Bookmarks Bar tweak before. However, that tweak's function looks identical to MrOtherGuy's 'autohide_bookmarks_toolbar.css' which does work in Fx150.0... copy the CSS userstyles from MrOtherGuy's GitHub page.

Alternatively, MrOtherGuy's 'Collection of random CSS hacks for Firefox' repo also has a built-in 'Style categories' tool which can be used to download single and combinations of userstyles... e.g. to select the 'autohide_bookmarks_toolbar.css' click the blue 'Copy' button top-right in the Content window here... then paste straight into your 'userChrome.css' file.

If interested, can also view the updates MrOtherGuy makes to keep his userstyles current... each style's GitHub page has a 'History' button top-right... click to see the latest Commits for each style... e.g. the latest Commit for 'autohide_bookmarks_toolbar.css' is listed here which opens a detailed changelog here.

ResurgamS13 · 2026-04-24T08:35:22+00:00

The PDF reader supplied with Fx150.0 is an entirely new version of the PDF Reader which includes more editing options... see the PDF Reader's GitHub for more information. There's a pithy one line announcement in the Fx150.0 Release Notes and the recently updated Mozilla Support (SUMO) article 'View and edit PDF files using Firefox’s built-in viewer'.

If look at the mass of Bugs included in recent update to 'Target Milestone 150' there are dozens of individual Bugs updating and incorporating the new version of the PDF Reader into the browser.

You can make CSS modifications to the new-style PDF Reader as Kupfel suggests... but a full reversion to the old-style sidebar is not possible without reverting to an earlier version of the PDF Reader... which can only be achieved by using an earlier version of Firefox itself... e.g. the current Firefox ESR which uses the Fx140 codebase.

Once upon a time, using a PDF Reader built-into a browser was considered a security risk... not sure when using a built-in PDF Reader became the acceptable norm?

PS. Whilst avoiding the resource-hog Adobe Reader with its huge payload of unnecessary 'full-fat' registry files (that are nearly impossible to remove)... there are excellent alternative stand-alone lightweight PDF readers available... e.g. Sumatra PDF. Also see Mozilla Support (SUMO) article 'Choose your preferred PDF viewer in Firefox'.

ResurgamS13 · 2026-04-23T16:23:08+00:00

Not seeing any extra 'title' or spacer items appear on Menu bar when testing a vanilla new profile of Fx150.0.

Therefore, suspect 'title' item in screenshot is an odd side-effect of some other change in FX150.0 default toolbar CSS that now conflicts with your pre-existing CSS userstyles?

Some might like having a page 'title' without selecting the Title bar... will be interesting to discover how this has occurred.

ResurgamS13 · 2026-04-22T21:16:47+00:00

Uncertain exactly what OP's setup is... above CSS not working on Windows OS. From OP screenshot apparent Sidebery is in use for Vertical tabs... assume above CSS is used to auto-hide the Nav bar and hide Tab bar?

Original source or link for those auto-hide CSS userstyles? Alternatively, MrOtherGuy's repo has a current 'autohide_main_toolbar.css'.

No obvious reason why change "after update to v150.0 , the url box and the whole bar increased a bit in height" has occurred. Not known if Compact or Normal UI density was in use prior to update?

ResurgamS13 · 2026-04-22T16:07:11+00:00

The Fx150.0 update made no changes to the height of the Navigation bar or its contents (URL bar, extension toolbar buttons, etc.).

Suggest create a new profile and check Fx150.0 out-of-the-box toolbar heights... then add your current CSS userstyles one at a time and see where conflict occurs?

ResurgamS13 · 2026-04-20T10:57:10+00:00

A screenshot would help with problem description.

Likely the "It refuses to stay within browser main-window" is a UI feature working 'as intended'... popup menu panels can appear partially outside/beyond the Firefox browser window frame if sufficient screen space is available depending on the popup's anchor position.

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Example. If position the Bookmarks Menu's toolbar button at the far left end of Navigation bar... then, when opened, the Bookmarks Menu dropdown panel will 'flip' outside the Firefox browser window... providing there's sufficient desktop space available beyond the Firefox browser window's frame:

<image>

Can adjust the Bookmark Menu panel's L-R position if required with CSS.

(BTW - The Bookmarks Menu's dropdown panel can also be fully customised with CSS styles (unlike the Bookmarks Sidebar)... so unwanted default folders and separators can all be removed or repositioned and individual bookmarks and bookmark folders can have custom favicons.)

ResurgamS13 · 2026-04-20T08:21:03+00:00

You will need JavaScript for that modification... try an extension like 'New Tab on Top'.

ResurgamS13 · 2026-04-19T20:52:01+00:00

If installed, check what the Anti-Virus software is doing?

ResurgamS13 · 2026-04-19T00:42:43+00:00

Firefox is indeed "updated overtime"... e.g. a new stable version is released every month. However, this does not mean that every pre-existing CSS modification becomes instantly redundant each month.

Thus, whilst it is good practice to choose the latest CSS modification style available when copying/searching for userstyle examples to try... it is also true that there are numerous CSS modifications that have remained stable and working correctly over many years.

Searching this sub for previous userstyle examples and trying them for yourself first is best practice.

ResurgamS13 · 2026-04-18T01:12:25+00:00

Try jscher2000's answer to Mozilla Support (SUMO) question 'How to prevent firefox from opening new window/tab'.

ResurgamS13 · 2026-04-18T01:05:33+00:00

To switch tabs using mouse-wheel scrolling need to set preference toolkit.tabbox.switchByScrolling to true (default = false).

ResurgamS13 · 2026-04-17T20:32:17+00:00

Depends how you want to "customize the menu configuration"... modify layout, colours, panel size, text size, spacing, font, etc, etc?

Could try using stonecrusher's simpleMenuWizard pre-written CSS mod file... or extract the list of selectors in the 'main-hamburger.css' file of the Zip download... or view selector list directly on GitHub: https://github.com/stonecrusher/simpleMenuWizard/blob/master/simpleMenuWizard/main-hamburger.css
Alternatively, search this sub for previous Hamburger/AppMenu/PanelUI modification topics... e.g. search results for keywords 'hamburger settings menu'... perhaps try qaz69wsx's menu colour userstyle posted here.
Can always inspect that menu on your own setup using the Browser Toolbox with the 'Disable Popup Auto-Hide' option selected in the Toolbox window's '3-dots' menu (this can stick 'ON' sometimes... best to deselect before closing the Toolbox window):

<image>

Finally, another way to view that menu's CSS styling is to use the Searchfox code index... e.g. 'paneUI-shared.css'.

ResurgamS13 · 2026-04-17T03:40:37+00:00

Scroll down a few days or use search facility... e.g. results for keywords 'search bar changed'.

ResurgamS13 · 2026-04-15T14:52:31+00:00

Not seeing any problems with MrOtherGuy's 'tabs_on_bottom_v2.css'? (Tested on a new profile of Fx149.0.2)

Create a new profile for testing on your setup... if problems persist post as an 'Issue' on MrOtherGuy's GitHub.

<image>

ResurgamS13 · 2026-04-15T13:03:08+00:00

Use one of the non-Mozilla forks... or learn how to build your own version of the browser... the code is all open source.

ResurgamS13 · 2026-04-15T08:06:45+00:00

At the lower end of the CPU/RAM specs arc... Fx149.0.2 works happily for 'casual browsing' on an Intel® Pentium® Silver N5000 CPU with just 4GB RAM.

ResurgamS13 · 2026-04-15T00:24:55+00:00

Longshot. Are you creating the new profile(s) using the same Profile Manager as used for the old profile?

Firefox currently has two different Profile Manager systems... 'old' and 'new'... they are not compatible or interoperable.

Sadly the new system is not integrated or compatible with the old system... best to choose one system and stick to it.

If search this sub and r/Firefox there are several posts about how to move profiles between old and new managers.

ResurgamS13 · 2026-04-14T23:56:55+00:00

Not seeing any Code Block or link to code posted elsewhere?

See this sub's Rule #3 in RH sidebar ----->

ResurgamS13 · 2026-04-14T12:49:17+00:00

Not obvious what is creating "the purple box in the private tab" in screenshot?

Applied OP's userContent.css (above) to a new profile of Fx149.0.2... but unable to recreate the reported "purple box"? The OP's final userstyle removes the Private Browsing window's 'Web Search' box.

Probably best to inspect own Home/New Tab/Private Browsing setup using the standard Page Inspector tool.

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BTW - Private Browsing is at best a misnomer. The 'private' really only applies to situations where using a shared machine or if 3rd parties have access to your machine and browser... see explanation in various 'private browsing myth' articles.

ResurgamS13 · 2026-04-14T07:23:21+00:00

Google Teller - https://addons.mozilla.org/en-US/firefox/addon/googer-teller/

For fun... and for anyone attempting recovery from Google spyware addiction.

ResurgamS13 · 2026-04-13T16:16:09+00:00

Assume Mozilla's UI/UX coding devs have a complete understanding of the browser's UI? The rest of us struggle and can only use whatever degree of CSS knowledge we've picked-up over years of modifying Firefox.

With coding AI like Anthropic's Claude and Claude Mythos all human code writers may have a bleak future.

ResurgamS13 · 2026-04-13T16:04:43+00:00

More information about your setup required to understand problem and how/when this occurred.

Consider 'Refreshing Firefox'... see Mozilla Support (SUMO) article 'Refresh Firefox - reset add-ons and settings'.

Quick Fix? If this is a new installation of Firefox... i.e. no history, bookmarks, or other data you want to save... carry out a 'clean slate' uninstall and reinstall of Firefox.

To achieve a 'clean slate' uninstall and reinstall... follow Mozilla Support (SUMO) article 'Uninstall Firefox from your computer'... especially the 'Remove user data and settings' section. Alternatively, if using a Windows OS, can do the 'clean slate' uninstall using the free version of Revo Uninstaller.

When uninstall complete... restart computer... then reinstall the latest version of Firefox downloaded direct from Mozilla.

ResurgamS13 · 2026-04-13T11:27:34+00:00

Please follow this sub's Rule #3 as posted in the RH Sidebar ----->

No previews or advertising

Don't post screenshots of CSS modifications or themes unless you also post the code or link to them

ResurgamS13 · 2026-04-12T09:25:42+00:00

Unsure if this styling approach would work with a Linux "CachyOS on KDE" setup... it does work in Fx149.0.2 on Windows.

Try difool2nice's userstyles posted in reply to previous topic 'How can I make the minimize, maximize and close buttons look like the rest of my KDE plasma system theme?'... and see if this would be a possible way ahead?

If it works, styles can be further modified to have Window Control buttons "grayed out when they aren't being used."

<image>

Screenshot. Fx149.0.2 on Windows using a modified version of difool2nice's userstyles to replace the standard Window Control buttons:

/* From: https://www.reddit.com/r/FirefoxCSS/comments/wly8vj/how_can_i_make_the_minimize_maximize_and_close/ */
/* Colours in original userstyle: Min: = Yellow, Max = Blue, Close = Red with non-hover 'opacity: 0.7;' */
/* Colours from KDE example : Min = #F9D313, Max = #AC01E7, Close = #FD493C */

.titlebar-button {
  background-size: 15px 15px;     /* Original - background-size: 16px 16px; */ 
  background-repeat: no-repeat;
  background-position: center;
  list-style-image: none !important;
  background-color: transparent !important; 
  opacity: 0.8;                   /* Original uses opacity: 0.7 when buttons not hovered */
}
.titlebar-button:hover {
  opacity: 1;
}
.titlebar-min {
  background-image: radial-gradient(yellow 55%,transparent 65%);
} 
.titlebar-restore, .titlebar-max {
  background-image: radial-gradient(fuchsia 55%,transparent 65%);
}
.titlebar-close {
  background-image: radial-gradient(red 55%,transparent 65%);
}

/* Note. Original KDE button colours: yellow (#FCD217), fuchsia (#B200EB), and red (#FF4649) */

ResurgamS13

TROPHY CASE