57 introduced a new pref called `browser.tabs.tabMinWidth` and set it by default to 100px. The default before 57 was 50px. You can go to about:config, proceed through the warning, search for the above pref, double click it, and set it to `50`

The tab width seems smaller now. Does changing it to 50px from 100px fix this?

https://www.reddit.com/r/firefox/comments/74983i/new_minwidth_default_in_todays_nightly/

tl;dr Yesterday we made a change in nightly such that the Firefox tabstrip will not start scrolling until roughly double the number of tabs has been opened, and we want your feedback.

Why did we do this? We've seen some feedback that a key advantage to chrome's behaviour here is that the user can see a larger number of tabs visible and distinguish between them. Chrome never overflows tabs, it just keeps opening more until the tab titles become unreadable. Firefox on the other hand starts hiding tabs off screen once tabs hit 100px wide by default. This new patch changes this to instead start hiding tabs at 50px instead, and introduces an about:config preference called browser.tabs.tabMinWidth. The work is tracked in bug 1404465.

Making the tab width smaller makes the content for a large number of tabs unreadable, unless I put the mouse pointer right over the tab, and I am not used to having to do that. It makes some of the tabs no more readable than Google Chrome is. I do like the ability to scroll tabs. I just want them readable, like they used to be. I would rather have some of them hidden, than others unreadable.

The tab width was 75. Changing it to 50 made the tabs smaller. Setting to 95 makes it look right. By the way is there a way, is there a way to have the tabs on the bottom? Until today, they were, but the add-on Classic Theme Restorer has now been disabled. I noticed that browser.tabs.on.Top is false, yet the tabs are on top. I did not change that. Is there a way to put tabs on the bottom?

Sorry, didn't see your last reply until after clicking Post

I'm not sure whether you went into about:config after getting the first reply. Here is the "step by step":

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste tabmin and pause while the list is filtered

(3) Double-click the browser.tabs.tabMinWidth preference and enter the desired value. I think 100 would match Firefox 56. You can go higher if you like.

(Values lower than 50 are ignored, for anyone trying to reduce the minimum, you'll need to use a custom style rule in a userChrome.css file for that.)

wworonick said

Is there a way to put tabs on the bottom?

Yes, using custom style rules. Here's the short method:

(A) You need to create a new chrome folder in your profile folder. This article has the steps for that (#1, #2, and optionally #3)

https://www.userchrome.org/how-create-userchrome-css.html

(B) Download the following file and move it into that chrome folder:

https://www.userchrome.org/samples/userChrome-tabs_on_bottom.css

(C) Rename the file to just userChrome.css

The next time you quit Firefox and start it up again, it should discover that file and apply the rules.

There are more elaborate rules from the author of Classic Theme Restorer you can try if that doesn't quite do it.