A few months back, I did an upgrade of my Fedora 25. Everything went fine, except that I lost scrollbars on SeaMonkey. Since then, I Googled several times and couldn't find the cause or how to fix it, so I left it to be fixed on its own with my next upgrade.
That upgrade came last night, and now I'm running Fedora 27, but the problem persists. The desktop environment I use is xfce (currently, version 4.12.1). I'm not even sure what other data I should provide.
The problem appears only in SeaMonkey (in every page in which I'd expect a scrollbar to appear). Chrome, Firefox, Terminal, Skype,... all have their scrollbars.
Anyone knows how to get scrollbars in SeaMonkey to appear again?
Update: I just noticed that I do get a scroll bar under Metal Lion SeaMonkey theme. Its weirdly styled scrollbar even remains on the page after I switch to other themes (but doesn't appear in new tabs).
I tried several other themes, but it didn't pan out, and I really don't like this one. I'd prefer to stay with the "Modern" theme, but with scrollbars.